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Sunday Times Brain Teaser 737

by G.H. Dickson

Our old watchmaker works weekdays 9.30 am to 5 pm as regular as, well, clockwork. I recently asked him to adjust two 8-day striking clocks – the sort which, when fully-wound, will run for nearly eight days. They were keeping different times and each was wrong by an exact number of minutes per day, both less than an hour.

He immediately wound the clocks fully and set them to the right time,  which was an exact number of minutes after the hour. He then put them on a shelf for later observation.

The next Monday, when he went to take the clocks down to adjust them, he found that both were simultaneously starting to strike 8 o’clock, which was some hours plus an exact number of minutes past the correct time.

What day and exact time was it when he originally set them?

One Comment Leave one →
  1. brian gladman permalink

    Using a routine from my number theory library

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