All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars
 perplexus dot info

 Got a Minute? (Posted on 2003-09-10)
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)

Comments: ( Back to comment list | You must be logged in to post comments.)
 short and sweet | Comment 27 of 35 |
It is impossible. 25 min = 60*(5/12), and all possible fractions that result in the manipulation of the timers are of the form 60*(x/2^k) – where both x and k are positive integers – thus any addition of the fractions will always give a denominator that is a power of 2, thereby eliminating the possibility of having a 5/12 fraction of an hour.
 Posted by Eric on 2003-11-07 17:57:49

 Search: Search body:
Forums (0)