Pipes A, B and C can fill an empty tank $\frac{30}{7}$ hours, if all the three pipes are opened simultaneously. A and B are filling pipes and C is an emptying pipe. Pipe A can fill the tank in 15 hours and pipe C can empty it in 12 hours. In how long (in hours) can pipe B alone fill the empty tank?
Answer & explanation
Correct answer: option 4
A + B + C = \(\frac{30}{7}\) hrs,
A+ = 15 hrs,
C- = 12 hrs,
⇒ A + B + C = 14, (Efficiency)
⇒ 4 + B - 5 = 14,
⇒ B - 1 = 14,
⇒ B+ = 15 units,
Time required by B to completely fill the cistern alone = \(\frac{60}{15}\) = 4 hrs.