Problem 15 · 2025 Math Kangaroo
Medium
Arithmetic & Operations
sum-constraint
Theo is on a treadmill and sees two stopwatches. The left one shows the time elapsed since he started his workout; the right one shows the time remaining until the end. At the moment shown the left reads 14:58 and the right reads 21:32. At some point both stopwatches will display the same time. What will they display then?
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Answer: D — 18:15
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Hint 1 of 2
One clock counts up and the other counts down at the same speed, so their sum stays constant.
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Hint 2 of 2
They show the same time exactly halfway through that constant total.
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Approach: the two readings always sum to the full workout time
- Elapsed + remaining is constant: 14:58 + 21:32 = 36:30 (the whole workout).
- They are equal at half of that total: \(36{:}30 \div 2 = 18{:}15\), which is (D).
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