# Pumping

The tank is filled with a larger pump in 12 hours and with scond pump in 15 hours. For how long does the tank fill when both pumps are switched on at the same time?

Correct result:

t =  6.667 h

#### Solution:

$a=1/12=\dfrac{ 1 }{ 12 } \doteq 0.0833 \ \\ b=1/15=\dfrac{ 1 }{ 15 } \doteq 0.0667 \ \\ t=1/(a+b)=1/(0.0833+0.0667)=\dfrac{ 20 }{ 3 }=6.667 \ \text{h}$

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