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Five bells first begin to toll together and then at intervals of 5, 10, 15, 20 and 25 seconds respectively. After what interval of time will they toll again together?

Correct answer: A. 5 min

  • A. 5 min
  • B. 5.5 min
  • C. 5.2 min
  • D. None

Explanation

The bells meet again after the least common multiple of their intervals. LCM(5, 10, 15, 20, 25) = 300 seconds, and 300 seconds ÷ 60 seconds per minute = 5 minutes. The likely mistake is option c, 5.2 minutes, caused by treating the intervals as an average rather than finding their LCM.

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