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Spring 2009 Week 5

Suppose at midnight (12:00 am) you are handed two sandglasses, one which measures a minutes and one which measures b minutes.  (Assume that all of the sand is at the bottom of the sandglasses at midnight.)  Explain if and how you can use the two sandglasses to determine when it is 12:15 am, for each of the following choices of a and b:

No.    a    b
1    5    8
2    4    6
3    7    11
4    7    10
5    4    7
6    4    9