Tap P can fill a cistern in 6 hours and tap Q can empty the cistern in 20 hours. If both taps are kept opened simultaneously, then the time taken by both to fill the cistern:
Answer & explanation
Correct answer: option 2
Total work = efficiency × time
Total efficiency = 10 - 3 = 7
Both ( P + Q ) will take time → \(\frac{60}{7}\) = \(\frac{60}{7}\) hours