A clock is 5 minutes slow at 12 noon on Monday and 3 minutes fast at 8 p.m. on Tuesday. It gains at a steady rate. When did it show the correct time?

12 midnight on Monday nightCorrect answerYour answer6 a.m. on TuesdayCorrect answerYour answer8 a.m. on TuesdayCorrect answerYour answer4 p.m. on TuesdayCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer C

Correct answer: C

From noon Monday to 8 p.m. Tuesday is 32 hours, and the clock went from 5 minutes slow to 3 minutes fast: a gain of $5 + 3 = 8$ minutes.
Rate $= 8 \div 32 = \frac{1}{4}$ minute per hour, that is 1 minute every 4 hours.
It was correct once it had gained 5 minutes: $5 \times 4 = 20$ hours after noon Monday, which is 8 a.m. on Tuesday.

Worth noting

12 midnight uses the 3 minutes instead of the 5 (the clock must first make up the 5 minutes it was slow). 4 p.m. Tuesday takes the halfway point of the 32 hours.

Concept: When a steadily gaining clock is exactly right
Typical timeTypical: 75 s
Your timeYours: —

The rule this testsClocks that gain or lose

Practise this chapter →

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

A clock is 5 minutes slow at 12 noon on Monday and 3 minutes fast at 8 p.m. on Tuesday. It gains at a steady rate. When did it show the correct time?

Explanation