Monday, March 12, 2012

Measure 9 minutes

You are given two hourglasses. One measures 4 minutes and one measures 7 minutes. How would you measure exactly 9 minutes?
Posted by at 1:57 AM
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1 comment:

  1. SudMarch 12, 2012 at 2:01 AM

    ime 4m timer 7 minute timer
    0 min Start Start
    4 mins Flip 3 minutes left
    7 mins 1 m left Flip
    8 mins Stop Flip (1 minute left)
    9 mins Stop

    In this approach only 3 inverts are required.

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