Pipes A and B can fill an empty tank in 12 minutes and 18 minutes respectively. The tank is empty and both pipes are opened together for 3 minutes and then closed. What part of the tank is still empty?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(\frac{7}{12}\)
Find the part filled in 3 minutes; the part still empty is the rest of the tank.
Part filled in one minute \(\displaystyle =\frac{1}{12}+\frac{1}{18}=\frac{3+2}{36}=\frac{5}{36}\)
Part filled in 3 minutes \(\displaystyle =3\times\frac{5}{36}=\frac{5}{12}\)
Part still empty \(\displaystyle =1-\frac{5}{12}=\frac{7}{12}\)