Multiple choice

A watch was set right at 7 am. It gains 5 seconds in 3 minutes. In the afternoon of the same day, when the watch indicated 4:15, the true time was

  1. 3:55 pm

  2. 4:00 pm

  3. 4:05 pm

  4. 4:10 pm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The watch gains 5 seconds every 3 minutes. In 1 hour (60 minutes), it gains (5/3) * 60 = 100 seconds. From 7 am to 4:15 pm is 9 hours and 15 minutes = 555 minutes. Total gain = (5/3) * 555 = 925 seconds = 15 minutes and 25 seconds. If the watch shows 4:15, the true time is 4:15 - 15m 25s = 3:59:35 pm, which is approximately 4:00 pm.

AI explanation

If the watch indicates 9 hours and 15 minutes (555 minutes) have passed, we calculate the real time elapsed using the proportion of real time to watch time. Because the watch covers 180 seconds of real time in 185 seconds of watch time, the real time elapsed is (180 / 185) multiplied by 555 minutes, which equals 540 minutes. Adding 540 minutes, or 9 hours, to 7 am gives a true time of 4:00 pm.

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