Problem 6 · 2021 Math Kangaroo
Easy
Algebra & Patterns
arithmetic-sequence
A measuring tape is wound around a cylinder. What number should be at the place shown by the question mark?
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Answer: C — 69
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Hint 1 of 2
The tape spirals upward, so going straight up one full loop adds the same fixed amount each time.
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Hint 2 of 2
Find how much the numbers jump per loop, then add that jump to the value just below the '?'.
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Approach: add one loop's increment
- Each full wrap around the cylinder covers the same stretch of tape, so a mark sits the same amount above the mark directly beneath it.
- The 27 sits directly above the 6 one loop down, so one loop is worth 27 − 6 = 21.
- The question mark is two loops above the 27, landing on 27 + 21 + 21 = 69.
Mark:
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