Three pipes A, B and C can fill an empty tank together in 8 hours. After working at it together for 2 hours B is closed and A and C can fill the remaining part in 9 hours. Pipe B can fill the empty tank in :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 24 hours
Consider the part of the tank filled in one hour: A, B and C together fill \(\frac{1}{8}\) of the tank per hour.
In the first 2 hours they fill
\( \displaystyle 2 \times \frac{1}{8} = \frac{1}{4} \)
The remaining \(\frac{3}{4}\) is filled by A and C in 9 hours, so A and C together fill per hour
\( \displaystyle \frac{3}{4} \div 9 = \frac{1}{12} \)
Hence B alone fills per hour
\( \displaystyle \frac{1}{8} - \frac{1}{12} = \frac{3 - 2}{24} = \frac{1}{24} \)
So pipe B alone fills the tank in 24 hours.