Question

I dont understamd this problem please help------!

A work crew has a new pump and an old pump. The new pump can fill a tank in 5 hours, and the old pump can fill the same tank in 7 hours. Write and solve and equation for the time it will take both pumps to fill one tank of the pumps are used together.

Answer 1

Hello,

Let's
`D_1\ the \ outflow\ of\ the\ new\ pump\\ D_2\ the \ outflow\ of\ the\ old\ pump\\\\ V \ the\ volume \of\ the\ tank\\\\ D_1*5=V==\ \textgreater \ D_1= (V)/(5) \\ D_2*7=V==\ \textgreater \ D_2= (V)/(7) \\ D_1+D_2= (V)/(5)+ (V)/(7) \\ D_1+D_2= (7*V)/(35)+ (5*V)/(35) \\ D_1+D_2= (12V)/(35) \\ Time \ for \ the \2 \pumps=V=(D_1+D_2)*(35)/(12)==>2H55min`