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Question 315312: Two college students have started their own business building computers from kits. Working alone, one student can build a computer in 20 hours. When the second student helps, they can build a computer in 7.5 hours. How long would it take the second student, working alone, to build the computer.
Answer by nerdybill(7384)   (Show Source):
You can put this solution on YOUR website! Two college students have started their own business building computers from kits. Working alone, one student can build a computer in 20 hours. When the second student helps, they can build a computer in 7.5 hours. How long would it take the second student, working alone, to build the computer.
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Let x = time it takes second student to build it alone
then
7.5(1/20 + 1/x) = 1
Multiplying both sides by 20x:
7.5(x + 20) = 20x
7.5x + 150 = 20x
150 = 12.5x
12 hours = x
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