Two inlet pipes A and B can fill a tank in 18 hours and 24 hours, respectively, while an outlet pipe C can empty the full tank in X hours. Initially, all three pipes are opened together. After 8 hours, pipe B is closed, and another 6 hours later, pipe C is also closed. The remaining portion of the tank is then filled by pipe A alone. If the tank gets completely filled in a total of 16 hours, find the value of X.
Solution
✅ Correct Option: 3
Pipe A works for all 16 hours, pipe B for the first 8 hours, and outlet C for the first 14 hours. Without pipe C, the amount filled is $\dfrac{16}{18}+\dfrac{8}{24}=\dfrac{8}{9}+\dfrac{1}{3}=\dfrac{11}{9}$ of the tank. Since the tank is exactly full, pipe C must remove $\dfrac{11}{9}-1=\dfrac{2}{9}$ of the tank in 14 hours. $\dfrac{14}{X}=\dfrac{2}{9}$ $X=63$ hours.