# 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?

Result

t =  6.667 h

#### Solution:

$a = 1/12 = \dfrac{ 1 }{ 12 } \doteq 0.0833 \ \\ b = 1/15 = \dfrac{ 1 }{ 15 } \doteq 0.0667 \ \\ t = 1/(a+b) = 1/(0.0833+0.0667) = \dfrac{ 20 }{ 3 } \doteq 6.6667 = 6.667 \ \text{ h }$

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