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The broken clock

The broken clock

My watch is delayed 5 seconds every hour. Last Saturday at 00:00 I put it on time and just a week later at the same time I have to adjust it again.

How many minutes will I have to advance the clock to set it up again?

Solution

In a week, there are 7 days, which are 24 * 7 = 168 hours. Since every hour delays 5 seconds, it will be delayed 168 * 5 = 840 seconds, which is 840/60 = 14 minutes, so the clock will indicate exactly 23:46, that is, I will have to advance it 14 minutes to put it on time at 00:00.