Problem 5 · 2017 Math Kangaroo
Easy
Arithmetic & Operations
total-then-divide
How many white squares need to be coloured in black, so that there are exactly twice as many white squares as there are black squares?
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Answer: B — 3
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Hint 1 of 2
Count the squares in the grid, then count how many are already black.
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Hint 2 of 2
If the whites are to be twice the blacks, then out of every 3 squares exactly 1 is black.
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Approach: split the grid into thirds: one third must end up black
- The grid has 24 squares in all.
- Twice as many white as black means 1 of every 3 squares is black, so 24 ÷ 3 = 8 squares must be black.
- There are already 5 black squares, so colour 8 − 5 = 3 more.
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