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The cold-water faucet of a bath tub can fill the tub in 15 minutes. The drain, when opened, can empty the full tub in 20 minutes. Suppose the tub is empty and the faucet and drain are both opened at the same time. How long will it take to fill the tub?

 Feb 4, 2019

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Each minute 1/15  of the tub is filled  and 1/20 of the tub is drained

 

So.....the portion of the tub that is fillied  every minute is (1/15 - 1/20)  = [ 20 - 15 ]  / 300 =  5 /300 = 1/60 of the tub

 

Therefore.....it must take 60 minutes to fill he tub when both are opened

 

 

cool cool cool

 Feb 4, 2019

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