<PRE><B>Question 181182</B>
there are 810 dishes that need to be rinsed. john can rinse them in 135 minutes by himself it will take his friend bob 90 minutes to rinse these dishes how lomg will it take them if they rinse the 810 dishes together?
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John DATA:
time = 135 min/job ; rate = 1/135 job/min
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Bob DATA:
time = 90 min/job ; rate = 1/90 job/min
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Together DATA:
time = x min/job ; rate = 1/x job/min
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Equation:
rate + rate = together rate
1/135 + 1/90 = 1/x

Multiply thru by 90*135*x
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90x + 135x = 90*135

225x = 90*135
x = 54 min (time to do the job together)
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Cheers,
Stan H.</PRE>