🦘 Math Kangaroo Grade All Felix 1-2 Ecolier 3-4 Benjamin 5-6 Kadett 7-8 Junior 9-10 Student 11-12 ⇄ switch contest
Mock Test

Mock Test (random)

30 problems — one per position, pulled from random authored years. Hints and solutions are locked until you submit. Retake as often as you want — every attempt is saved to your test history (if you're logged in).

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Problem 1 · 2020 Math Kangaroo Easy
Spatial & Visual Reasoning tiling-tessellationsequence-of-figures

Which tile below completes the wall shown next to it?

Figure for Math Kangaroo 2020 Problem 1
Show answer
Answer: E
Show hints
Hint 1 of 2
Look at the cells right around the empty hole and see how their pink shapes point into it.
Still stuck? Show hint 2 →
Hint 2 of 2
The missing tile must continue the four-fold pinwheel pattern; match the orientation of the dark corners and pink star to the neighbours.
Show solution
Approach: match the missing tile to the surrounding pattern
  1. The wall is built from a repeating tile, rotated in a pinwheel; the hole sits where one tile is missing.
  2. Read off what the neighbouring cells demand at the four edges of the hole.
  3. Only choice E has its dark corner and pink-star orientation matching every neighbour, so it completes the wall.
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Problem 2 · 2009 Math Kangaroo Easy
Number Theory last-digit

Which of the following numbers is even?

Show answer
Answer: D — 200 × 9
Show hints
Hint 1 of 2
A number is even when its value ends in an even digit — work out each option's value.
Still stuck? Show hint 2 →
Hint 2 of 2
Multiplying anything by an even number gives an even result.
Show solution
Approach: evaluate each option
  1. 2009 is odd; 2+0+0+9 = 11 is odd; 200−9 = 191 is odd; 200+9 = 209 is odd.
  2. 200 × 9 = 1800, which is even.
  3. So the even one is 200 × 9 — answer D.
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Problem 3 · 2021 Math Kangaroo Easy
Spatial & Visual Reasoning path-tracing

In the square you can see the digits from 1 to 9. A number is created by starting at the star, following the line and writing down the digits along the line while passing. For example, the line shown represents the number 42685. Which of the following lines represents the largest number?

Figure for Math Kangaroo 2021 Problem 3
Show answer
Answer: E
Show hints
Hint 1 of 2
Read off the digit string each path makes, then compare them as numbers.
Still stuck? Show hint 2 →
Hint 2 of 2
The biggest number starts with the largest leading digit; break ties by the next digit.
Show solution
Approach: trace each path into a number and compare
  1. Each option traces a path from the star across cells of the 1-9 grid, writing the digit of every cell it passes.
  2. Convert each path to its number and compare digit by digit from the left.
  3. Path E produces the largest such number.
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Problem 4 · 2010 Math Kangaroo Easy
Logic & Word Problems off-by-one

A staircase has 21 steps. Nick and Mike count the steps, one from bottom to top and the other from top to bottom. They meet at one step, which Nick counts as the 10th. Which number does Mike give this same step?

Show answer
Answer: C — the 11th
Show hints
Hint 1 of 2
They both count the very same step, just starting from opposite ends.
Still stuck? Show hint 2 →
Hint 2 of 2
On a 21-step staircase, think about how many steps sit below the meeting step and how many sit above it.
Show solution
Approach: count the same step from the other end
  1. The two boys meet on one shared step on a staircase of 21 steps.
  2. Mike counts that step from the top: the steps above it plus the meeting step itself make up his count, which lands on the 11th.
  3. So Mike calls the meeting step the 11th — the answer is C.
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Problem 5 · 2010 Math Kangaroo Easy
Counting & Probability careful-counting

Anna has connected every upper point to every lower point with straight lines. How many lines has she drawn?

Figure for Math Kangaroo 2010 Problem 5
Show answer
Answer: C — 30
Show hints
Hint 1 of 2
Count the dots on top and the dots on the bottom.
Still stuck? Show hint 2 →
Hint 2 of 2
Each top dot sends one line to every bottom dot, so think about repeated addition (or multiplying).
Show solution
Approach: multiply the two groups of dots
  1. There are 5 dots on top and 6 dots on the bottom.
  2. Each of the 5 top dots is joined to all 6 bottom dots, so we have 6 lines repeated 5 times.
  3. That is \(5 \times 6 = 30\) lines — the answer is C.
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Problem 6 · 2024 Math Kangaroo Medium
Geometry & Measurement foldingreflectionsymmetry
Figure for Math Kangaroo 2024 Problem 6
Show answer
Answer: C
Show hints
Hint 1 of 2
The paper is transparent, so after folding you see both the original marks and their mirror images together.
Still stuck? Show hint 2 →
Hint 2 of 2
Reflect the holes and lines across the dashed fold line and overlay them on the side that stays put.
Show solution
Approach: reflect across the fold and overlay
  1. Folding along the dashed line lays one half onto the other; since the paper is see-through, each mark and its mirror image both show.
  2. Reflect the holes and the zig-zag line across the fold line and combine them with the marks already there.
  3. The resulting pattern of holes and lines matches choice C.
  4. So the folded paper looks like C.
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Problem 7 · 2014 Math Kangaroo Easy
Arithmetic & Operations division

Katrin has 38 matches. She uses all of them to make a triangle and a square that share no matches. Each side of the triangle is made of 6 matches. How many matches are in one side of the square?

Show answer
Answer: B — 5
Show hints
Hint 1 of 2
Work out how many matches the triangle uses, then see what is left for the square.
Still stuck? Show hint 2 →
Hint 2 of 2
Whatever the square gets, split it evenly across its four equal sides.
Show solution
Approach: subtract the triangle's matches, then divide the rest by 4
  1. The triangle has three sides of 6 matches, so it uses 3 × 6 = 18 matches.
  2. That leaves 38 − 18 = 20 matches for the square.
  3. The square's four equal sides share these, so each side has 20 ÷ 4 = 5 matches.
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Problem 8 · 2024 Math Kangaroo Medium
Logic & Word Problems work-backwardcasework
Figure for Math Kangaroo 2024 Problem 8
Show answer
Answer: C
Show hints
Hint 1 of 2
A box can be moved only when nothing sits on it, so the order boxes become free is fixed by the starting picture.
Still stuck? Show hint 2 →
Hint 2 of 2
For each tower, check whether a box ends up under another box that was still trapped when it had to be placed; that ordering conflict makes a tower impossible.
Show solution
Approach: check the forced unloading order against each tower
  1. From the start, only the top boxes are free; a box can be placed under another only if that other box was already moved.
  2. Read each target tower from the bottom up and see whether every box placed below another could have been freed and set down before the box on top of it.
  3. Tower C requires putting a box beneath one that was still pinned at that moment, which the rules forbid.
  4. So the worker cannot build tower C.
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Problem 9 · 2017 Math Kangaroo Medium
Geometry & Measurement area-fraction

A rectangle is twice as long as it is wide. What fraction of the rectangle is shaded grey?

Figure for Math Kangaroo 2017 Problem 9
Show answer
Answer: B — \(\tfrac38\)
Show hints
Hint 1 of 2
Slice the rectangle along its diagonals and midline and compare the shaded triangles to the whole.
Still stuck? Show hint 2 →
Hint 2 of 2
Add up the grey pieces as a fraction of the full rectangle.
Show solution
Approach: split the rectangle into two equal squares and add the grey pieces
  1. The rectangle is twice as long as wide, so it splits down the middle into two equal squares.
  2. In the left square the grey is one triangle that is exactly half the square.
  3. In the right square the grey triangle is half of a half, so a quarter of that square.
  4. Grey is \(\tfrac12 + \tfrac14 = \tfrac34\) of one square, out of the two squares, so the shaded fraction is \(\tfrac34 \div 2 = \tfrac38\) — option (B).
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Problem 10 · 2016 Math Kangaroo Medium
Spatial & Visual Reasoning composition

Robert has two equally big squares made of paper. He glues them together. Which of the following shapes can he not make?

Figure for Math Kangaroo 2016 Problem 10
Show answer
Answer: A — The house/pentagon shape (A).
Show hints
Hint 1 of 3
He may slide one square so the squares touch along an edge or just at a corner, but each square keeps its size and square shape.
Still stuck? Show hint 2 →
Hint 2 of 3
Try to draw two equal squares hidden inside each answer shape.
Still stuck? Show hint 3 →
Hint 3 of 3
The shape that cannot be cut back into two equal squares is the impossible one.
Show solution
Approach: try to split each outline back into two equal squares
  1. Gluing two equal squares (along a full edge, a partial edge, or at a corner) can make four of the shapes.
  2. But the house shape has slanted roof edges that no straight-sided square can produce, so it cannot be cut back into two equal squares.
  3. So the shape he cannot make is the house, choice (A).
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Problem 11 · 2023 Math Kangaroo Medium
Geometry & Measurement perimetergrid

A terrace is covered with square tiles of different sizes. The smallest tile has a perimeter of 80 cm. A snake lies along the edges of the tiles (see picture). How long is the snake?

Figure for Math Kangaroo 2023 Problem 11
Show answer
Answer: C — 420 cm
Show hints
Hint 1 of 3
A square's perimeter is four equal sides, so first turn the 80 cm into the length of one small-tile side.
Still stuck? Show hint 2 →
Hint 2 of 3
Use that small side as your ruler and walk along the snake, counting how many small sides fit into each straight stretch.
Still stuck? Show hint 3 →
Hint 3 of 3
Add up all the little side-lengths the snake covers, then multiply by the length of one side.
Show solution
Approach: find the small-tile side, then count how many of those lengths the snake covers
  1. The smallest tile is a square with perimeter 80 cm, so each of its sides is 80 / 4 = 20 cm.
  2. Reading the snake's path along the tile edges, it stretches across 21 of these small side-lengths.
  3. So the snake is 21 × 20 cm = 420 cm long.
  4. The answer is C, 420 cm.
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Problem 12 · 2022 Math Kangaroo Medium
Geometry & Measurement area

A box-shaped water tank measures 4 m × 2 m × 1 m, and the water in it is 25 cm deep. The tank is then turned onto its side (see the picture on the right). How high is the water in the tank now?

Figure for Math Kangaroo 2022 Problem 12
Show answer
Answer: D — 1 m
Show hints
Hint 1 of 2
The amount of water does not change — only the shape of the space it fills.
Still stuck? Show hint 2 →
Hint 2 of 2
Find the water's volume, then divide by the area of the new bottom face to get the new height.
Show solution
Approach: the volume stays the same, so divide by the new base
  1. The water's volume is 4 × 2 × 0.25 = 2 m³ (using 25 cm = 0.25 m).
  2. After tipping, the tank rests on a 1 m × 2 m face, so the new bottom has area 2 m².
  3. Height = volume ÷ base = 2 ÷ 2 = 1 m.
  4. So the answer is D.
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Problem 13 · 2021 Math Kangaroo Medium
Spatial & Visual Reasoning path-tracing

Rosa wants to start at the arrow, follow the line, and get out at the other arrow. Which piece is it NOT possible to put in the middle to obtain that?

Figure for Math Kangaroo 2021 Problem 13
Show answer
Answer: D
Show hints
Hint 1 of 2
The middle piece must connect the line entering it to the line leaving it within the surrounding grid.
Still stuck? Show hint 2 →
Hint 2 of 2
Check each candidate's openings against the fixed track around the centre; one cannot link them up.
Show solution
Approach: match the centre piece's connections to the fixed track
  1. The path must enter the centre square and leave it so the whole route runs from arrow to arrow.
  2. The surrounding cells fix which sides of the centre the line must touch.
  3. Piece D cannot join those required sides, so it is the impossible one.
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Problem 14 · 2018 Math Kangaroo Hard
Logic & Word Problems casework

The two girls Eva and Olga and the three boys Adam, Isaac, and Urban play together with a ball. When a girl has the ball she throws it either to the other girl or to a boy. Every boy throws the ball only to another boy, but never back to the boy it just came from. The first throw is made by Eva to Adam. Who makes the 5th throw?

Show answer
Answer: A — Adam
Show hints
Hint 1 of 2
After Eva throws to Adam, the ball stays among the three boys, and a boy never throws back to whoever just threw to him.
Still stuck? Show hint 2 →
Hint 2 of 2
Track who holds the ball before each throw; the no-return rule on three boys forces the 5th thrower.
Show solution
Approach: trace the holder, using the no-immediate-return rule
  1. Throw 1 is Eva to Adam, so Adam makes throw 2.
  2. From then on the ball moves only among the three boys, each time to a boy other than the one who just passed it.
  3. On a triangle of three boys this no-return rule sends the ball Adam -> (a boy) -> (the third boy) -> back to Adam.
  4. So the maker of the 5th throw is Adam.
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Problem 15 · 2012 Math Kangaroo Medium
Geometry & Measurement perimeterarea

The figure on the right has a perimeter of 42 cm. The figure was made from eight equally sized squares. What is the area of the figure?

Figure for Math Kangaroo 2012 Problem 15
Show answer
Answer: D — 72 cm²
Show hints
Hint 1 of 2
The whole boundary is made of equal little square-sides; count how many of them go around.
Still stuck? Show hint 2 →
Hint 2 of 2
Find one square's side from the perimeter, then the area is 8 of those squares.
Show solution
Approach: find the unit side from the perimeter, then total area
  1. The outline of the figure is made of 14 equal square-edges, so 14 x (side) = 42 cm.
  2. That gives one side = 42 / 14 = 3 cm.
  3. Each small square has area 3 x 3 = 9 cm², and there are 8 of them: 8 x 9 = 72 cm².
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Problem 16 · 2013 Math Kangaroo Hard
Logic & Word Problems casework

In the last hockey game there were lots of goals. In the first half 6 goals were scored in total and the visiting team was leading. In the second half the home team scored another three goals and won the match. How many goals did the home team score in total?

Show answer
Answer: C — 5
Show hints
Hint 1 of 3
In the first half the two teams together scored 6, and the visitors were ahead.
Still stuck? Show hint 2 →
Hint 2 of 3
List the first-half scores where visitors lead: 6-0, 5-1 or 4-2.
Still stuck? Show hint 3 →
Hint 3 of 3
Then add the home team's 3 second-half goals and see which case lets them win.
Show solution
Approach: test first‑half splits that let home win
  1. First half the goals add to 6 with visitors ahead, so the splits are visitors 6 home 0, visitors 5 home 1, or visitors 4 home 2.
  2. The home team then scores 3 more; to win they need their total above the visitors' 6, 5, or 4.
  3. Only 4-2 works: home ends with \(2 + 3 = 5\) against 4, a win, so the home team scored 5 in total, choice C.
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Problem 17 · 2011 Math Kangaroo Hard
Geometry & Measurement spatial-reasoning

You are given the three corner points of a triangle and want to add a fourth point to make the four corners of a parallelogram. In how many places can the fourth point be placed?

Show answer
Answer: C — 3
Show hints
Hint 1 of 2
Draw the triangle, then try sliding the new point off each of the three corners in turn.
Still stuck? Show hint 2 →
Hint 2 of 2
Each corner of the triangle can be the one that sits opposite the new point — count those choices.
Show solution
Approach: let each triangle corner be the one opposite the new point
  1. Draw the triangle with corners A, B, C; the fourth point joins them into a parallelogram.
  2. Pick which corner is opposite the new point: if it is A you get one parallelogram, if B another, if C a third.
  3. That gives three different spots for the fourth point, so the answer is 3.
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Problem 18 · 2018 Math Kangaroo Hard
Number Theory place-value

Instead of digits, Hannes uses the letters A, B, C, and D in a calculation. Different letters stand for different digits, and the addition ABC + CBA = DDDD is correct (each group of letters is a number written with those digits in order). Which digit does the letter B stand for?

Show answer
Answer: A — 0
Show hints
Hint 1 of 2
Add ABC and CBA column by column and notice the symmetry of the outer digits.
Still stuck? Show hint 2 →
Hint 2 of 2
The sum 101(A + C) + 20B must equal a four-digit repdigit DDDD; only D = 1 fits, which pins B.
Show solution
Approach: add by place value and match to a repdigit
  1. ABC + CBA = 100(A+C) + 20B + (A+C) = 101(A+C) + 20B.
  2. This must equal DDDD = 1111 x D, and since the sum is below 2000 we need D = 1, so 101(A+C) + 20B = 1111.
  3. Taking A + C = 11 gives 1111, leaving 20B = 0.
  4. So B stands for 0.
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Problem 19 · 2020 Math Kangaroo Hard
Algebra & Patterns sum-constraintsubstitution

Beatriz has five sisters whose ages are 2, 3, 5, 8, 10 and 17. Beatriz writes these ages in the circles of the diagram so that the sum of the ages in the four corners of the square equals the sum of the ages in the four circles in the horizontal row. What is this sum?

Figure for Math Kangaroo 2020 Problem 19
Show answer
Answer: D — 32
Show hints
Hint 1 of 2
The left and right circles belong to both groups, so when you set the two sums equal those two ages cancel out.
Still stuck? Show hint 2 →
Hint 2 of 2
That leaves top + bottom = centre + far-right; find the split of the six ages that makes this work, then add up the four corners.
Show solution
Approach: cancel the two shared circles, then place the rest
  1. The corners (top, left, right, bottom) and the horizontal row (left, centre, right, far-right) share the left and right circles, so equal sums mean the unshared pairs match: top + bottom = centre + far-right.
  2. Among 2, 3, 5, 8, 10, 17 the pairs 3 + 10 and 5 + 8 both make 13, so put 3 and 10 at top and bottom, and 5 and 8 at centre and far-right.
  3. That leaves 2 and 17 for the shared left and right circles. Each sum is then (left + right) + (the matching 13) = (2 + 17) + 13 = 32.
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Problem 20 · 2010 Math Kangaroo Stretch
Counting & Probability careful-counting

In a pizzeria there is a basic pizza with tomato and cheese. It can be ordered with exactly one or exactly two of the following toppings: anchovies, artichokes, mushrooms or capers. The pizza comes in three sizes. How many different types of pizza are offered in total?

Show answer
Answer: A — 30
Show hints
Hint 1 of 2
Count the topping choices first: either pick one topping, or pick a pair of two toppings.
Still stuck? Show hint 2 →
Hint 2 of 2
Once you know how many topping choices there are, each one comes in 3 sizes.
Show solution
Approach: count topping choices, then multiply by sizes
  1. Picking one topping: 4 ways. Picking a pair from the 4 toppings: the pairs are \(\{1,2\},\{1,3\},\{1,4\},\{2,3\},\{2,4\},\{3,4\}\), so 6 ways.
  2. That is \(4 + 6 = 10\) topping choices.
  3. Each choice comes in 3 sizes, so \(10 \times 3 = 30\) pizzas — the answer is A.
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Problem 21 · 2013 Math Kangaroo Stretch
Algebra & Patterns custom-operation

Starting from three numbers, the ‘addition machine’ makes three new ones by adding each pair together. For example, from {3, 4, 6} it makes {10, 9, 7}, and running it again gives {16, 17, 19}. We feed in the three numbers {20, 1, 3} and run the machine 2013 times. What is the biggest possible difference between two of the three resulting numbers?

Show answer
Answer: D — 19
Show hints
Hint 1 of 3
Don't follow the numbers themselves; watch the gaps between them.
Still stuck? Show hint 2 →
Hint 2 of 3
Work out the gaps in the example before and after one run of the machine and notice they are the same three gaps.
Still stuck? Show hint 3 →
Hint 3 of 3
If the gaps never change, the biggest gap at the end is the biggest gap you start with.
Show solution
Approach: watch the gaps between the numbers, not the numbers
  1. Check the example: \(\{3,4,6\}\) has gaps 1, 2, 3, and after the machine \(\{7,9,10\}\) has gaps 2, 1, 3 — the very same three gaps, just shuffled.
  2. So the three gaps between the numbers never change, no matter how many times you run the machine.
  3. Starting from \(\{20,1,3\}\) the biggest gap is \(20 - 1 = 19\), and it is still 19 after 2013 runs, which is choice D.
Another way:
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Problem 22 · 2015 Math Kangaroo Stretch
Number Theory divisibilitycasework

A train has 12 carriages. In each carriage there is the same number of compartments. Mike is sitting in the 18th compartment behind the engine, this is in the 3rd carriage. Joanna is sitting in the 50th compartment behind the engine, this is in the 7th carriage. How many compartments are in one carriage?

Show answer
Answer: B — 8
Show hints
Hint 1 of 3
Every carriage holds the same number of compartments, so try the answer choices one at a time.
Still stuck? Show hint 2 →
Hint 2 of 3
If each carriage has 8 compartments, carriages 1 and 2 use compartments 1–16, so carriage 3 holds 17–24.
Still stuck? Show hint 3 →
Hint 3 of 3
Check that the same guess also lands compartment 50 inside carriage 7.
Show solution
Approach: test the answer choices: find how many compartments fit before each carriage
  1. Try 8 compartments per carriage. Then carriages 1 and 2 fill compartments 1 through 16, so carriage 3 holds compartments 17 through 24 — and Mike's seat 18 lands there. ✓
  2. With 8 each, carriages 1–6 fill compartments 1 through 48, so carriage 7 holds 49 through 56 — and Joanna's seat 50 lands there. ✓
  3. Both facts work only with 8, so there are 8 compartments in one carriage.
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Problem 23 · 2020 Math Kangaroo Stretch
Logic & Word Problems caseworkwork-backward

A panel has 4 circles. When Lucy touches a circle, that circle and every circle touching it switch colour (white ↔ black), as shown. Starting with all circles white, at least how many circles must Lucy touch, one after another, to make all four black?

Figure for Math Kangaroo 2020 Problem 23
Show answer
Answer: C — 4
Show hints
Hint 1 of 2
Touching a circle flips it and its neighbours; each circle must end flipped an odd number of times.
Still stuck? Show hint 2 →
Hint 2 of 2
Find the smallest set of touches making every circle's flip-count odd.
Show solution
Approach: make every circle flip an odd number of times
  1. Touching a circle toggles it and its neighbours; all four start white and must end black (odd flips each).
  2. One or two touches cannot make all four flip an odd number of times.
  3. The fewest touches achieving this is 4 (touching each circle once works).
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Problem 24 · 2021 Math Kangaroo Stretch
Logic & Word Problems casework

An apple and an orange weigh as much as a pear and a peach. An apple and a pear weigh less than an orange and a peach, and a pear and an orange weigh less than an apple and a peach. Which of the pieces of fruit is the heaviest?

Show answer
Answer: C — peach
Show hints
Hint 1 of 2
Turn each sentence into an inequality between sums of two fruits.
Still stuck? Show hint 2 →
Hint 2 of 2
Combine the inequalities to rank the fruits and spot the heaviest.
Show solution
Approach: combine the weight inequalities
  1. The balance apple + orange = pear + peach rearranges to peach = apple + (orange − pear).
  2. The two 'weigh less' facts force pear to be lighter than both apple and orange, so orange − pear is positive.
  3. Then peach = apple + (a positive amount) beats apple, and likewise peach beats orange, so the heaviest is peach.
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Problem 25 · 2021 Math Kangaroo Stretch
Geometry & Measurement symmetry

What is the smallest number of shaded squares that can be added to the diagram to create a design, including the grid, with 4 axes of symmetry?

Figure for Math Kangaroo 2021 Problem 25
Show answer
Answer: E — 21
Show hints
Hint 1 of 2
Four axes of symmetry means both diagonals and both midlines must mirror the shading.
Still stuck? Show hint 2 →
Hint 2 of 2
Reflect the two shaded cells across all four axes and count every new cell those reflections demand.
Show solution
Approach: enforce all four mirror symmetries
  1. A design with 4 axes of symmetry must look the same under both diagonal flips and both horizontal/vertical flips.
  2. Reflecting the two already-shaded cells through all those symmetries generates a full set of matching cells.
  3. The number of extra cells that must be shaded to complete that symmetric set is 21.
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Problem 26 · 2020 Math Kangaroo Stretch
Number Theory divisibilitydigit-sum

A three-digit number is called balanced if its middle digit is the average of the other two digits. How many balanced numbers are divisible by 18?

Show answer
Answer: C — 6
Show hints
Hint 1 of 2
Divisible by 18 means even and digit-sum divisible by 9; 'balanced' means the middle is the average of the outer two.
Still stuck? Show hint 2 →
Hint 2 of 2
Balanced makes the digit sum three times the middle digit, so the middle digit must be a multiple of 3.
Show solution
Approach: combine the balanced condition with divisibility by 18
  1. Balanced means middle = (first+last)/2, so the digit sum first+middle+last = 3 x middle.
  2. Divisible by 9 needs that sum divisible by 9, so the middle digit is 0, 3, 6 or 9; divisible by 2 needs an even last digit.
  3. Listing the cases gives 234, 432, 468, 630, 666, 864 - exactly 6 numbers.
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Problem 27 · 2021 Math Kangaroo Stretch
Algebra & Patterns substitutionsum-constraint

Each shelf holds a total of 64 deciliters of apple juice. The bottles come in three different sizes: large, medium and small (see picture). How many deciliters of apple juice does a medium bottle contain?

Figure for Math Kangaroo 2021 Problem 27
Show answer
Answer: D — 10
Show hints
Hint 1 of 2
Let large, medium, small bottles hold L, M, S deciliters; each shelf's bottles total 64.
Still stuck? Show hint 2 →
Hint 2 of 2
Write one equation per shelf and solve the system for M.
Show solution
Approach: set up one equation per shelf and solve
  1. Counting bottles, the three shelves give 3L + 4S = 64, 2L + 2M + 3S = 64, and 4M + 6S = 64.
  2. Solving the system gives S = 4, L = 16 and M = 10.
  3. So a medium bottle contains 10 deciliters.
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Problem 28 · 2021 Math Kangaroo Stretch
Spatial & Visual Reasoning cube-viewscasework

A large cube has side-length 7 cm. On each of its 6 faces, the two diagonals are drawn in red. The large cube is then cut into small cubes with side-length 1 cm. How many small cubes will have at least one red line drawn on it?

Show answer
Answer: B — 62
Show hints
Hint 1 of 2
A red face-diagonal only marks the unit cubes it passes through on that face; count by face then remove double counts.
Still stuck? Show hint 2 →
Hint 2 of 2
Edge and corner cubes can be crossed by diagonals on more than one face — don't count them twice.
Show solution
Approach: count marked cubes per face, then correct overlaps
  1. Each face is a 7×7 grid of little squares; the two diagonals run through 7 + 7 − 1 = 13 of them (the centre square is shared).
  2. Six faces give 6 × 13 = 78, but cubes along the edges and corners get a red line on two faces and were counted twice — there are 16 such double-counts.
  3. So the number of unit cubes with at least one red line is 78 − 16 = 62.
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Problem 29 · 2020 Math Kangaroo Stretch
Spatial & Visual Reasoning foldingpaper-cutting

Vania has a sheet of paper divided into nine equal squares. She folds it as shown — first the horizontal folds, then the vertical folds — until the coloured square is on top of the stack. She wants to write the numbers 1 to 9, one per square, so that after folding they read in order from top to bottom, starting with 1 on top. On the unfolded sheet shown, which numbers should she write in places a, b and c?

Figure for Math Kangaroo 2020 Problem 29
Show answer
Answer: Ca = 7, b = 5, c = 3
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Hint 1 of 2
Track where each unfolded square ends up in the stack after the horizontal then vertical folds.
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Hint 2 of 2
Reverse the folds to read which numbers land at positions a, b and c on the flat sheet.
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Approach: reverse the fold order to map stack layers to grid cells
  1. Folding horizontally then vertically stacks the nine squares; the coloured square is on top (number 1), and lower layers get 2,3,...
  2. Unfolding to the flat sheet, each layer returns to its cell, spreading the numbers in a fixed pattern.
  3. Reading positions a, b, c gives a = 7, b = 5, c = 3 - option C.
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Problem 30 · 2020 Math Kangaroo Stretch
Logic & Word Problems careful-countingcasework

The map shows some islands connected by bridges. A navigator wants to visit each island exactly once. He started at Cang Island and wants to finish at Uru Island, and he has just reached the black island in the centre. In which direction must he go now to be able to complete his route?

Figure for Math Kangaroo 2020 Problem 30
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Answer: C — South.
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Hint 1 of 2
He has to visit every island exactly once, so the move he makes now must not strand any island he still needs to reach.
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Hint 2 of 2
If he picks a direction that walks him into a dead-end corner before the rest are visited, he can never get back; only one direction keeps a path open all the way to Uru.
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Approach: choose the only move that leaves a single-visit path to Uru
  1. He must pass through each island once and finish at Uru, so from the centre he cannot step toward any group of islands he would later be unable to leave.
  2. Going North, East or West leads him into a part of the map he would have to enter or leave twice, leaving some island unvisited.
  3. Heading South is the one move that still lets him reach every remaining island exactly once and end at Uru.
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