<PRE><B>Question 388892</B>
let t=time for smaller pipe to fill tank
let t-1 =time for larger pipe to fill tank
let c=tank capacity
==
Given
small pipe rate = 20 liters per minute
large pipe rate=25 liters per minute
==
use formula: tank capacity=rate * time
--
small pipe;  tank capacity c=20*t
large pipe:  tank capacity c=25*(t-1)
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since tank capacity is the same for both pipes
20*t=25*(t-1)
20*t=25*t-25
25=5*t
5=t
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answer:  it takes the small pipe 5 minutes to fill the tank

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