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Got a Minute? (Posted on 2003-09-10) Difficulty: 3 of 5
You have an infinite amount of timers, each is an hour long (they do not have dials on telling you how long they've been going - they just beep when the time is up). You can set it to double speed at any time, but you cannot set it back to normal speed (eg if you set it to double speed at the start it will last 30 minutes.

Using each timer only once, is it possible to time exactly 25 minutes?

If it is, what is the smallest number of timers you need to do this, and the quickest time you can acheive it?

No Solution Yet Submitted by Lewis    
Rating: 3.6000 (15 votes)

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Solution | Comment 22 of 35 |
the correct answer to this puzzle is no, you cannot time exactly 25 minutes since you ate limites to only fractions with denominations in powers of 2, and 25, is 5/12, which does not have a power of two for a deniminator using an infinite number of timers it is possible to refine your time closer and closer and get increasingly more acurate, but as you are cutting the value in half each time, after a point the variance will be so little as to be insignificant, but it is an exponetial equation that approaches, but never reaches the 25 minute mark.
  Posted by Matthew on 2003-10-09 17:22:33
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