A clock with an ordinary 12-hour dial (no a.m./p.m. shown) gains 5 minutes every hour. It is set right at 6 a.m. on a Monday. When will its dial next show the correct time?

6 a.m. on SundayCorrect answerYour answer6 a.m. on the following MondayCorrect answerYour answer6 p.m. on SundayCorrect answerYour answer6 a.m. on Saturday of the following weekCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer A

Correct answer: A

A 12-hour dial shows the correct time again when the clock is exactly 12 hours $= 720$ minutes ahead.
At 5 minutes per hour this takes $720 \div 5 = 144$ hours $= 6$ days.
6 days after 6 a.m. on Monday is 6 a.m. on Sunday.

Worth noting

Saturday of the following week waits for a 24-hour gain (12 days), but a 12-hour dial is right again after only 12 hours. The following Monday treats 144 hours as a full week; 144 hours is 6 days.

Concept: When a gaining clock is right again
Typical timeTypical: 120 s
Your timeYours: —

The rule this testsClocks that gain or lose

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Ten questions from Calendars and Clocks, at your own pace.

A clock with an ordinary 12-hour dial (no a.m./p.m. shown) gains 5 minutes every hour. It is set right at 6 a.m. on a Monday. When will its dial next show the correct time?

Explanation