Problem 6 · 2021 Math Kangaroo
Easy
Number Theory
place-valuecareful-counting
A measuring tape is wrapped around a cylinder. Which number should be at the place shown by the question mark?
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Answer: C — 48
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Hint 1 of 2
The tape is one long strip wrapped around, so the numbers keep counting up as you go round and round.
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Hint 2 of 2
Line up the marks directly below the ? with the row beneath it to see how far past the visible numbers it sits.
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Approach: continue the running count around the cylinder to the ? mark
- Each time the tape wraps once around, the number jumps by the same amount: the band 1…10 sits below the band 22…31, so one wrap adds 21.
- The ? sits one wrap above the 27 on the band below it.
- 27 + 21 = 48.
- So the number is 48 (C).
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