Multiple choice

A clock is set right at 10 p.m. The clock gains 20 minutes in 12 hours. What will be the right time when the clock indicates 10 a.m. on the following day?

  1. 9:39 a.m.

  2. 9:41 a.m.

  3. 10:21 a.m.

  4. 10:19 a.m.

  5. 9:31 a.m.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The clock gains 20 minutes in 12 hours. This means for every 720 minutes of real time, the clock shows 740 minutes. The clock shows 10 a.m. the next day, which is 12 hours later. The ratio of real time to clock time is 720/740. Real time passed = 12 * (720/740) = 11 hours and 40.5 minutes. 10 p.m. + 11h 40.5m = 9:40.5 a.m.

AI explanation

The clock runs fast, so its 12 hours from 10 pm to 10 am equals exactly 720 minutes of real time plus the 20 extra minutes it gains. The ratio of real time to clock time is 720 divided by 740, which reduces to 36 over 37. When the defective clock shows 12 hours, or 720 minutes, the actual elapsed real time is 720 multiplied by 36 divided by 37, which is about 700.54 minutes, meaning the actual time is 9:40 am and 32 seconds. The closest choice is 9:41 am.

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