A pipe A can fill a tank in 4 hours. There are two outlet pipes, B and C, from the tank which can empty it in 8 and 10 hours respectively. If all the three pipes are opened simultaneously, how long will it take to fill the tank?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 40 hours
In one hour A fills \(\frac{1}{4}\) of the tank, while B and C empty \(\frac{1}{8}\) and \(\frac{1}{10}\) of it. The net part filled in one hour is
\( \displaystyle \frac{1}{4} - \frac{1}{8} - \frac{1}{10} \)
\( \displaystyle = \frac{10 - 5 - 4}{40} = \frac{1}{40} \)
So the tank is filled in 40 hours.