Work Rate problem help

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Work Rate problem help

by trickism » Sun Jul 25, 2010 7:03 am
It takes three laborers ten hours to install four faucets (each faucet takes the same amount of work to install)
How many hours would it take nine laborers to install twelve faucets?

a. 1/3
b. 3 1/3
c. 6
d. 10
e. 15


thanks in advance!
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by GMATGuruNY » Sun Jul 25, 2010 7:19 am
trickism wrote:It takes three laborers ten hours to install four faucets (each faucet takes the same amount of work to install)
How many hours would it take nine laborers to install twelve faucets?

a. 1/3
b. 3 1/3
c. 6
d. 10
e. 15


thanks in advance!
work = 12 faucets = (number of laborers) * (number of hours)

The number of laborers is inversely proportional to the number of hours. As the number of laborers goes up, the number of hours must go down, so that the amount of work (in this case, 12 faucets) stays the same. When two values are inversely proportional, their product is always the same.

(number of laborers) * (number of hours) = (number of laborers) * (number of hours)

3 laborers for 4 faucets = 10 hours.
So 3 laborers for 12 faucets = 3 * 10 = 30 hours.

To determine the number of hours required by 9 laborers:

3 * 30 = 9 * h
90 = 9h
h = 10

The correct answer is D.
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by trickism » Sun Jul 25, 2010 7:53 am
THANKS! that was extremely helpful!