Question

A pipe can fill a tank in 8 hours. After half the tank is filled, two more similar pipes are opened. What is the total time taken to fill the tank completely?

• A. 80 min
• B. 60 min
• C. 70 min
• D. 90 min

Answer 1

The correct option is A 80 min

Amount of work done or Part filled by one pipe in 1 hour = $\frac{1}{8}$
The tank is half-filled, therefore the amount to be filled = ½
After the tank is half-filled, three pipes of equal capacity begin to work.

Amount of work done or Part filled by three pipes in 1 hour = $\frac{3}{8}$
Time taken to fill the remaining half $\frac{1}{2}$ of the tank by three similar pipes will be = $\frac{\frac{1}{2}}{\frac{3}{8}}$
$\frac{1}{2}\times \frac{8}{3}=\frac{8}{6}\mathrm{of}\mathrm{an}\mathrm{hour}=\left(\frac{8}{6}\right)\times 60\mathrm{minutes}=80\mathrm{minutes}$