Two pipes A and B can fill a tank in 4 hours and 5 hours respectively. If they…
2025
Two pipes A and B can fill a tank in 4 hours and 5 hours respectively. If they are turned up alternatively for one hour each, then time taken to fill the tank is :
- A.
2 hours 15 minutes
- B.
4 hours 24 minutes
- C.
3 hours 21 minutes
- D.
4 hours 36 minutes
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Show answer & explanation
Correct answer: B
Solution:
Take the whole tank as 1 unit.
Rate of the pipe that fills in 4 hours = 1/4 tank per hour. Rate of the pipe that fills in 5 hours = 1/5 tank per hour.
In each two-hour cycle (first the 4-hour pipe for 1 hour, then the 5-hour pipe for 1 hour) they fill 1/4 + 1/5 = 9/20 of the tank.
After two such cycles (4 hours) they fill 2 × 9/20 = 9/10 of the tank.
Remaining to fill = 1 − 9/10 = 1/10. The faster pipe (the one that fills in 4 hours) fills at 1/4 tank per hour, so time required = (1/10) ÷ (1/4) = 2/5 hour = 24 minutes.
Total time = 4 hours + 24 minutes = 4 hours 24 minutes.
Answer: 4 hours 24 minutes