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Two large and 1 small pumps can fill a swimming pool in 4 hours. One large and 3 small pumps can also fill the same swimming pool in 4 hours. How many hours will it take 4 large and 4 small pumps to fill the swimming pool. (We assume that all large pumps are similar and all small pumps are also similar.)

 Jul 8, 2020
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1/(2L+s)   =4     and

 

1/(L+3s)=4         equating the denominators leads to L = 2s    subbing into one of the equations finds

                                       s = 1/20     so L = 2/20

 

now for FOUR of them

 

1 /( 4(2/20) + 4 (1/20) )    =     1/ (12/20) = 20 /12 = 1 2/3 hr   for 4 of each pump to fill the pool

 Jul 9, 2020

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