Two pipes, D and E, can fill a cistern in 26 and 78 hours, respectively, while working alone. If the two pipes are opened together, the time taken to fill the cistern is:
Answer & explanation
Correct answer: option 2
D+ = 26 hrs, E+ = 78 hrs,
⇒ Time required for D + E to fill the tank completely = \(\frac{78}{3+1}\) = \(\frac{78}{4}\) = $19 \frac{2}{4}$ = $19 \frac{1}{2}$ hours