Problem 16 · 2017 Math Kangaroo
Medium
Arithmetic & Operations
work-backwardcustom-operation
Which number must be written into the circle with the question mark so that the calculation is correct?
Show answer
Answer: B — 9
Show hints
Hint 1 of 2
Going all the way around the loop must bring you back to the same number.
Still stuck? Show hint 2 →
Hint 2 of 2
The x0 step forces one circle to be 0; start there and go around.
Show solution
Approach: use that the loop closes; the x0 step pins a value
- Following the arrows must return to the starting circle.
- One step is 'x0', whose result is 0, so the circle it leads to holds 0.
- From there: 0, then +6 gives 6, then x4 gives 24, then -15 gives the question mark.
- So the question mark is 24 - 15 = 9.
Mark:
· log in to save