Pumps

Four identical pumps fill the tank in 40 hours. How many pumps would we have to use if we wanted to save 8 hours?

Correct answer:

n =  1

Step-by-step explanation:

$$\begin{gathered} n_1=4 \\ t=40\cdot n_1=40\cdot 4=160 \\ n=t\mathrm{/}(40-8)-n_1=160\mathrm{/}(40-8)-4=1 \end{gathered}$$

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