Multiple choice general knowledge math & puzzles

A clock is set right at 8 a.m. The clock gains 10 minutes in 24 hours. What will be the true time when the clock indicates 1 p.m. on the following day?

  1. 48 min. past 12

  2. 38 min. past 12

  3. 28 min. past 12

  4. 25 min. past 12
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A Correct answer
Explanation

From 8 a.m. on one day to 1 p.m. on the following day is 29 hours of indicated clock time. Since the clock gains 10 minutes every 24 hours, 24 hours and 10 minutes (1450 minutes) of indicated time corresponds to 24 hours (1440 minutes) of true time. Therefore, 29 hours of indicated time corresponds to $29 \times (1440 / 1450) = 28.8$ hours of true time, which is 28 hours and 48 minutes. Adding 28 hours and 48 minutes to 8 a.m. gives 12:48 p.m., or 48 minutes past 12.

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