A clockmaker has three clocks: Clock X, Clock Y, and Clock Z. At noon, all three show 12:00. Clock X runs perfectly. Clock Y gains 5 minutes every real hour. Clock Z loses 10 minutes every real hour. When Clock Y shows 3:15, what time does Clock Z show?
2:00
Clock Y gains 5 minutes per hour, so it advances 65 minutes for every 60 real minutes. Clock Y showing 3:15 means 195 minutes have elapsed on Clock Y. Dividing 195 by 65 gives 3 real hours elapsed since noon. In 3 real hours, Clock Z (which advances 50 minutes per hour) moves forward by 150 minutes (2 hours and 30 minutes? Wait: 60 - 10 = 50 minutes per hour. 3 * 50 = 150 minutes = 2 hours 30 minutes... Wait! 12:00 + 2h 30m = 2:30). Let's double check: 3 * 50 = 150 mins = 2:30 PM.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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