Problem 14 · 2017 Math Kangaroo
Stretch
Arithmetic & Operations
off-by-onecareful-counting
A kangaroo always does ten jumps within a minute. Then he has a three minute break. How many minutes does it need in order to do 50 jumps?
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Answer: D — 17
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Hint 1 of 2
50 jumps means 5 separate one-minute jumping sessions; count the breaks BETWEEN them.
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Hint 2 of 2
There is no break after the last session, so there is one fewer break than sessions.
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Approach: add jumping minutes and the breaks between sessions
- 10 jumps per minute, so 50 jumps need 5 one-minute jumping sessions.
- Between the 5 sessions there are 4 breaks of 3 minutes each (no break after the last).
- Total time = 5 jumping minutes + 4 breaks of 3 minutes = 5 + 12 = 17 minutes.
- So it needs 17 minutes.
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