<PRE><B>Question 215962</B>
    An old water pump can fill up a large trough in 10 minutes, but a second, newer pump takes only 3 minutes and 20 seconds to fill the trough. How long would it take to fill the trough using both pumps at the same time?
.
Convert rate to seconds:
Old pump: 
fill trough per 10 minutes
is equivalent
fill trough per 600 seconds
.
New pump:
fill trough per 3 minutes  20 seconds
is equivalent
fill trough per 200 seconds
.
Let x = seconds it takes for both pump
then
x(1/600 + 1/200) = 1
Multiplying both sides by 600:
x(1 + 3) = 600
4x = 600
x = 150 seconds
.
So, for both pumps to fill the trough:
2 minutes 30 seconds
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