Pipes A and B can fill an empty tank in 9 minutes and 18 minutes respectively. The tank is empty, and both pipes are opened together for 4 minutes and then closed. What part of the tank is filled?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(\frac{2}{3}\)
The part filled is the one-minute work of both pipes together multiplied by the 4 minutes they run.
Part filled in one minute \(\displaystyle =\frac{1}{9}+\frac{1}{18}=\frac{2+1}{18}=\frac{3}{18}=\frac{1}{6}\)
Part filled in 4 minutes \(\displaystyle =4\times\frac{1}{6}=\frac{2}{3}\)
The pipes fill \(\frac{2}{3}\) of the tank.