Pipe P can fill a tank alone in 7 hours. Pipe Q can fill the same tank alone in 13 hours. In how much time can they together fill the tank?
Answer & explanation
Correct answer: option 4
P+ = 7 hrs,
Q+ = 13 hrs,
⇒ Time required by P + Q to fill the tank completely = \(\frac{91}{13+7}\) = \(\frac{91}{20}\) = \( {4 }_{20 }^{11 } \) hrs = 4 hrs 33 minutes.