Question 301609
    Barney can build a barn in 15 hours. david can build a barn in 10 hours. How long will it take for the barn to be built if they work together?
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Barney's rate: 1/15
David's rate: 1/10
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Let t = time it takes for both
then
t(1/15 + 1/10) = 1
Multiply both sides by 150:
t(10 + 15) = 150
25t = 150
t = 6 hours