A clock that gains 5 minutes every hour is set right at 8 a.m. Later the same day it shows 4:40 p.m. What is the correct time then?

3:55 p.m.Correct answerYour answer4:00 p.m.Correct answerYour answer4:35 p.m.Correct answerYour answer5:20 p.m.Correct answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer B

Correct answer: B

In every 60 true minutes this clock shows 65 minutes.
Since 8 a.m. it has shown 8 h 40 min $= 520$ minutes.
True time passed $= 520 \times \frac{60}{65} = 480$ minutes $= 8$ hours, so the correct time is 4:00 p.m.

Worth noting

3:55 p.m. treats 8 a.m. to 4:40 p.m. as 9 hours of gain. 5:20 p.m. adds the gain instead of removing it. The gain builds per TRUE hour, so convert with the ratio $60 : 65$ .

Concept: True time from the reading of a fast clock
Typical timeTypical: 75 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 that gains 5 minutes every hour is set right at 8 a.m. Later the same day it shows 4:40 p.m. What is the correct time then?

Explanation