Thursday, April 15, 2010

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 Administrator at 3:34 PM

1 comment:

  1. AnonymousNovember 29, 2011 at 9:10 AM

    Hourglass A = 4 mins
    Hourglass B = 7 mins
    1. Start both hourglasses
    2. When A ends, 4 mins have passed.
    3. Flip A. There are 3 more mins remaining in B.
    4. When B ends, 3 more mins have passed.
    5. Flip B. There is one more minute remaining in A.
    6. When A ends, 1 more minute has passed. There are 6 mins remaining in B.
    7. Flip B, and wait to end. 1 more minute will pass.

    Total = 4+3+1+1 = 9 minutes

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