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Work/rate

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Work/rate

by billyr » Sun Feb 22, 2009 11:23 am
Six machine each working at the same constant rate, together can completea certain job in 12 days. How many additional machine will be needed to complete job in 8 days?

a)2
b)3
c)5
d)6
e)8





Answer b, but how you set up the equation? thanks
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by sureshbala » Sun Feb 22, 2009 11:26 am
6 machines take 12 hours. So the work requires 72 machine-hours. To finish the same work in 8 hrs we need 72/8 = 9 machines. Hence 3 more machines are needed
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by billyr » Sun Feb 22, 2009 11:29 am
sureshbala wrote:6 machines take 12 hours. So the work requires 72 machine-hours. To finish the same work in 8 hrs we need 72/8 = 9 machines. Hence 3 more machines are needed
Thanks
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