Question

Two pipes can fill a tank in 10 hrs and 12 hrs each whereas a third pipe will empty the tank completely in 20 hrs. If all the three pipes work together, how long will it take for the tank to fill up?

• A. 7 hrs 30 min
• B. 7 hrs 40 min
• C. 7 hrs 50 min
• D. 8 hrs 30 min
• E. 7 hrs

Answer 1

The correct option is A

7 hrs 30 min

Net part filled in 1 hr = ($\frac{1}{10}$+ $\frac{1}{12}$ - $\frac{1}{20}$) = $\frac{2}{15}$

So, the tank will be full in $\frac{15}{2}$ hrs = 7 hrs 30 min.