Three pipes A, B and C can fill a tank in 5 hours, 8 hours and 10 hours…
2025
Three pipes A, B and C can fill a tank in 5 hours, 8 hours and 10 hours respectively. If they are turned up alternatively for one hour each, then time taken to fill the tank is :
- A.
5 hrs 30 mins
- B.
7 hrs 15 mins
- C.
6 hrs 45 mins
- D.
7 hrs 10 mins
Attempted by 2 students.
Show answer & explanation
Correct answer: C
Key idea: pipes A, B and C operate one hour each in the repeating order A → B → C.
Rates per hour: A = 1/5, B = 1/8, C = 1/10.
Amount filled in one full cycle (3 hours) = 1/5 + 1/8 + 1/10 = 17/40.
In 6 hours (two cycles) they fill 2 × 17/40 = 34/40 of the tank.
Remaining to fill = 1 − 34/40 = 6/40 = 3/20.
Next in the sequence is pipe A, which fills at 1/5 = 4/20 per hour. Time to fill the remainder = (3/20) ÷ (4/20) = 3/4 hour = 45 minutes.
Total time = 6 hours + 45 minutes = 6 hours 45 minutes.
Answer: 6 hours 45 minutes.