Tick Tock Bad Clock
Math brain teasers require computations to solve.
Your friend gave you a clock for your birthday, but unfortunately, it's very unreliable. This one gains exactly 12 minutes every hour.
It is now showing 10pm and you know that it was correct at midnight, when you set it.
If the clock stopped four hours ago, what is the correct time now?
Answer
Since the clock gains 12 minutes every hour, for every real hour that has passed 72 minutes will pass on the clock. It has been 22 fake hours from midnight to the time the clock stopped, so in order to find the number of real hours we must first find the number of fake minutes, then divide the number of fake minutes by the number of minutes that pass by in an hour for the clock (72) to find the number of real hours that have passed from midnight to when the clock stopped. The following shows arithmetic work:
22 x 60 = 1320 (clock minutes that have passed from midnight to when the clock stopped)
1320 / 72 = 18.333333... (real hours that have passed from midnight to when the clock stopped)
18.333333... hours = 18 hours 20 minutes. Therefore it was 6:20pm when the clock stopped. And because the clock stopped four hours ago, it is now 10:20pm!
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