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Interview Question


If you have two sand glass timers, one with 7 minutes worth

  of sand and another with 4 minutes worth of sand, how do you use both to precisely time 12 minutes?

Interview Answer

3 Answers


flip the one with 4 minutes three times.

MW on Feb 7, 2012

Flip the seven and four at the same time, once the four minute runs out flip the seven minute back over because it will have four minutes till it runs out again. Once that runs out, flip over the four minute sand glass again, and after that run out, twelve minutes is up

SF on Apr 28, 2012

start the 7 min and 4 min sandbox the same time, and filp the 4 min sandbox when its done, and flip the 4 min sandbox again when the 7 min sandbox is done, so now you have 1 min in the 4 min sandbox, then you 1 + 4 + 7 = 12

TC on Sep 13, 2012

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