SOLUTION: A roofing contractor estimates that he can shingle a house in 20 hours and that his assistant can do it in 30 hours. How long will it take them to shingle the house working togethe

Question 132053: A roofing contractor estimates that he can shingle a house in 20 hours and that his assistant can do it in 30 hours. How long will it take them to shingle the house working together? If you could explain how to do it, that would be great. Thanks.
Answer by edjones(8007) (Show Source): You can put this solution on YOUR website!
For work problems the secret is to add the reciprocals of the numbers.
contractor can do 1/20 of the job in 1 hr.
assistant can do 1/30 of the job in 1 hr.
1/20+1/30
=3/60+2/60
=5/60=1/12 of the job working together.
So, the job will take 12 hrs.
.
Ed

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