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2020 Math Kangaroo

Problem 15

Problem 15 · 2020 Math Kangaroo Hard
Ratios, Rates & Proportions proportion

Whenever the kangaroo goes up seven steps, the rabbit goes down three steps. When the kangaroo is on step number 56, on which step will the rabbit be?

Figure for Math Kangaroo 2020 Problem 15
Show answer
Answer: B — 76
Show hints
Hint 1 of 2
Every time the kangaroo climbs 7, the rabbit drops 3 — they move in step.
Still stuck? Show hint 2 →
Hint 2 of 2
Count how many groups of 7 the kangaroo climbed, then drop the rabbit 3 for each.
Show solution
Approach: count synchronized moves and apply the rabbit's drop
  1. Reaching step 56 means the kangaroo made 56 ÷ 7 = 8 climbs.
  2. In those same 8 moves the rabbit dropped 8 × 3 = 24 steps from 100, landing on 100 − 24 = 76.
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