What's the Correct Time?
Math brain teasers require computations to solve.
I recently gave a new watch to my friend for their birthday. However, as usual with my presents, it was quite useless, as it gains 6 minutes every hour. I set it using my own accurate clock at midnight, and the watch now shows 8:26 am. I know that it stopped 30 minutes ago, so what is the correct time now?
Answer
8:10 am.
Since the watch is gaining 6 minutes every hour, for every real hour that has passed, the watch will show 66 minutes. Since the watch shows 8:26 am, we know that 506 watch minutes have passed. This therefore equals 460 real minutes and hence 7 hrs and 40 minutes. The watch stopped 30 minutes ago, therefore the time must now be 8:10 am.
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Comments
doghouse270  
Mar 27, 2006
| didn't get it but was cool anyway  |
AZTTT
Mar 27, 2006
| That was fun, thanks!  good one! It can also be solved by adding the new watch's equivalent of 30 minutes (33) to the NW time and solving for a current NW 'time' of 8:59. |
OldChinaHand
Mar 27, 2006
| It took a while but it worked out. Good one.  |
zonarita
Apr 19, 2006
| Draw I don't usually like, or even do, the math teasers. This one was fun and you did a very good job explaining to us non math people how to get the right answer - thanks! |
RRAMMOHAN
Jun 03, 2006
| Nice and interesting. Got it! |
javaguru
Jan 27, 2009
| To make the solution a bit clearer for others: the watch is running at 66/60 = 11/10 normal speed, so 10/11 * 506 = 460 minutes passed while the watch was running. Add the 30 minutes and you see that it is 506 - (460 + 30) = 16 minutes earlier than the watch shows.
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