Pipes And Cisterns Questions & Answers

Question 16

Easy

A tap drips at a rate of one drop/sec. 600 drops make 100ml. The number of litres wasted in 300 days is:

A 3600 litres

B 4320 litres

C 4800 litres

D 5400 litres

Correct Answer: B

Explanation:

Total seconds in 300 days = 300 × 24 × 60 × 60 = 25,920,000 seconds. At 1 drop/sec, total drops = 25,920,000 drops. Volume per drop = 100 ml / 600 = 1/6 ml. Total volume wasted = 25,920,000 × (1/6) ml = 4,320,000 ml. In litres = 4,320,000 / 1000 = 4,320 litres.

Question 17

Medium

A tank is fitted with two inlet pipes A and B and an outlet pipe C. Pipe A can fill the empty tank in 12 minutes. While pipe B alone can fill it in 18 minutes. Pipe C can empty the full tank in 11 1/4 minutes. If all three pipes are opened simultaneously, in what time will the empty tank be filled?

A 18 minutes

B 20 minutes

C 30 minutes

D 36 minutes

Correct Answer: B

Explanation:

11(1/4) = 45/4 minutes. Let capacity = LCM(12, 18, 45/4) = 180 units. Rate of A = 180 / 12 = +15 units/min. Rate of B = 180 / 18 = +10 units/min. Rate of C = -180 / (45/4) = -16 units/min. Net filling rate = 15 + 10 - 16 = 9 units/min. Time to fill tank = 180 / 9 = 20 minutes.

Question 18

Easy

A cistern can be filled by two pipes A and B in 4 hours and 6 hours respectively. When full, the tank can be emptied by a third pipe C in 8 hours. If all the taps be turned on at the same time, the cistern will be full in

A 3(1/7) hours

B 3(3/7) hours

C 3(5/7) hours

D 4 hours

Correct Answer: B

Explanation:

Let cistern capacity = LCM(4, 6, 8) = 24 units. Rate of A = 24 / 4 = +6 units/hour. Rate of B = 24 / 6 = +4 units/hour. Rate of C = -24 / 8 = -3 units/hour. Net filling rate = 6 + 4 - 3 = 7 units/hour. Time to fill cistern = 24 / 7 = 3(3/7) hours.

Question 19

Easy

Two Pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?

A 14 minutes 20 seconds

B 14 minutes 40 seconds

C 15 minutes

D 15 minutes 20 seconds

Correct Answer: B

Explanation:

Let capacity = LCM(15, 20) = 60 units. Rate of A = 60 / 15 = 4 units/min. Rate of B = 60 / 20 = 3 units/min. In first 4 minutes, A and B fill: (4 + 3) × 4 = 28 units. Remaining capacity = 60 - 28 = 32 units. Time taken by B alone to fill remaining 32 units = 32 / 3 = 10 minutes 40 seconds. Total time from start = 4 minutes + 10 minutes 40 seconds = 14 minutes 40 seconds.

Question 20

Easy

If 20 taps can fill a tank in 14 hours, then in how many hours will 35 taps fill that tank?

A 6 hours

B 7 hours

C 8 hours

D 9 hours

Correct Answer: C

Explanation:

Total work = Number of taps × Hours = 20 × 14 = 280 tap-hours. With 35 taps, time taken = Total tap-hours / Number of taps = 280 / 35 = 8 hours.

Pipes and Cistern Practice Questions