Question 233890
    Andrew can lay carpet in a house in ten hours. If Mary helps him, they can get the carpet down in six hours. What is the number of hours it takes Mary to do the job by herself.
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Let x = number of hours Mary can do the job by herself
then
6(1/10 + 1/x) = 1
6/10 + 6/x) = 1
Multiplying both sides by 10x:
6x + 60 = 10x
60 = 4x
15 hours = x