A watch that gains uniformly, is two minutes slow at noon on Monday and is 4 minutes 48 seconds fast at 2 pm on the following Monday. When was the watch showing the correct time?
A watch that gains uniformly, is two minutes slow at noon on Monday and is 4 minutes 48 seconds fast at 2 pm on the following Monday. When was the watch showing the correct time?
Solution
The watch is 2 minutes slow at noon on Monday and 4 minutes 48 seconds fast at 2 pm on the following Monday. The watch gains uniformly (runs faster than actual time at a constant rate).
From noon Monday to 2 pm the following Monday:
Noon Monday to noon next Monday = 7 days = hours
Noon next Monday to 2 pm next Monday = 2 hours
Total time = hours
The watch went from 2 minutes slow to 4 minutes 48 seconds fast.
Total gain by the watch = min min sec
Converting to seconds: min seconds, min sec seconds
Total gain = seconds
The watch needs to gain 2 minutes (120 seconds) from the starting point to show correct time.
If 408 seconds are gained in 170 hours, then 120 seconds are gained in:
Time needed hours
hours
Starting from noon Monday, add 50 hours:
24 hours later → Noon Tuesday
48 hours later → Noon Wednesday
50 hours later → 2 pm Wednesday
Therefore, the watch shows the correct time at 2 pm on Wednesday.
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