Question

John has to fill a water tank in 2 hours 30 minutes and he used 6 pipes for that. How many pipes should he use to fill the tank in 1 hour?

• A. 10 pipes
• B. 12 pipes
• C. 15 pipes
• D. 20 pipes

Answer 1

The correct option is C 15 pipes

Let the number of pipes be y.

$\begin{array}{ccc}\text{Number of pipes}& 6& y\\ \text{Time (in minutes)}& 150& 60\end{array}$
The number of pipes and the time are inversely proportional.

AB = constant
$A_1\times B_1$ = $A_2\times B_2$

$6\times 150=y\times 60\frac{6}{y}=\frac{60}{150}$

$\Rightarrow y=\frac{6\times 150}{60}=15$

John has to use 15 pipes to fill the tank in 1 hour.