Question

$6$ pumps are required to fill a tank in $1$ hour $20$ minutes. How long will it take if only $5$ pumps of the same type are used?

Answer 1

Let the desired time to fill the tank be $x$ minutes. Thus, we have the following table:

Number of pumps	$6$	$5$
Time (in minutes)	$80$	$x$

Lesser the number of pumps, more will the time required by it to fill the tank.
So, this is a case of inverse proportion
Hence, $80\times 6=x\times 5$ [$x_1{y}_1=x_2{y}_2$)
or $\frac{80\times 6}{5}=x$
or $x=96$ minutes
Thus, time taken to fill the tank by $5$ pumps is $96$ minutes or $1$ hour $36$ minutes.