A watch which gains 5 seconds in 3 minutes was set right at 7 a.m. In the afternoon of the same day, when the watch indicated quarter past 4 o'clock, the true time is:
Solution
Correct Answer: Option A
Time from 7 am to 4.15 pm = 9 hrs 15 min = \(\frac{37}4\)hrs
3 min. 5 sec. of this clock = 3 min. of the correct clock.
Now 3min.5sec. is \(\frac{37}{720}\) hrs of this clock = 3 min.is \(\frac1{20}\)hrs of the correct clock
\(\frac{37}4\) hrs of clock = \(\left(\frac1{20}\times\frac{720}{37}\times\frac{37}4\right)\) hrs of the correct clock.
= 9 hrs of the correct clock.
The correct time is 9 hrs after 7 am. i.e., 4 pm.
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