Problem 20 · 2023 Math Kangaroo
Stretch
Logic & Word Problems
clock-calendarcasework
Five clocks are hanging on the wall. One clock is one hour ahead. Another one is one hour late and one is correct. Two clocks have stopped working. Which clock shows the correct time?
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Answer: D — D
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Hint 1 of 2
The fast, slow and correct clocks differ by exactly one hour from each other in a chain.
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Hint 2 of 2
Find three clocks whose times are consecutive hours; the middle one is correct.
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Approach: locate the +1, correct and -1 trio of consecutive-hour clocks
- The accurate clock, the one an hour fast, and the one an hour slow show three times spaced one hour apart.
- Only one set of three clock faces forms such a consecutive-hour chain.
- The middle time of that chain is the correct clock, shown in D.
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