A watch is 1 minute slow at 1 p.m. on Tuesday and 2 minutes fast at 1 p.m. on Thursday. When did it show the correct time?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 5 a.m. on Wednesday
The watch gains time at a steady rate, so the time it has gained grows in proportion to the time passed. It shows the correct time at the moment when it has gained just enough to wipe out its 1 minute of slowness.
From 1 p.m. Tuesday to 1 p.m. Thursday is 48 hours
In that time it goes from 1 minute slow to 2 minutes fast, a gain of \(1+2=3\) minutes, so it gains 1 minute every 16 hours
It is right once it has gained 1 minute: 16 hours after 1 p.m. Tuesday
1 p.m. Tuesday + 16 hours = 5 a.m. Wednesday