Three pipes A,B and C are attached to a tank. A and B can fill it in 15 and 20…
2024
Three pipes A,B and C are attached to a tank. A and B can fill it in 15 and 20 minutes respectively while C can empty it in 30 minutes. If A, B and C are kept open successively for 1 minute each, how soon will the tank be filled ?
- A.
12 minutes
- B.
48 minutes
- C.
36 minutes
- D.
42 minutes
Show answer & explanation
Correct answer: C
Answer: 36 minutes
Explanation:
Rates per minute: A fills 1/15 of the tank, B fills 1/20, and C empties 1/30 (so C's rate is -1/30).
In one full cycle (A for 1 minute, then B for 1 minute, then C for 1 minute) the net filled = 1/15 + 1/20 - 1/30 = 1/12 of the tank.
Number of such cycles to fill the entire tank = 1 ÷ (1/12) = 12 cycles.
Each cycle takes 3 minutes, so total time = 12 × 3 = 36 minutes.