Multiple choice

The time taken by pipe A to fill a water tank is 32 minutes. Pipes B and C can together fill the water tank in 12 minutes. If the water comes twice as fast as pipe A through pipe C, then find the time taken by pipes A and B together to fill the water tank.

  1. 19.6 minutes

  2. 19.2 minutes

  3. 18.8 minutes

  4. 18.4 minutes

  5. 17.2 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pipe A fills 1/32 of the tank per minute, and pipes B and C together fill 1/12 per minute. Since C works twice as fast as A, its rate is 1/16, so B's rate is 1/48. Thus A and B together fill 5/96 of the tank per minute, taking 19.2 minutes.

AI explanation

Using the LCM method, let the total tank capacity be 96 units. Pipe A fills at a rate of 3 units per minute, and since pipe C is twice as fast, it fills at 6 units per minute. Pipes B and C together fill the tank in 12 minutes, so their combined rate is 8 units per minute, making pipe B's rate 2 units per minute. Pipes A and B together have a combined rate of 5 units per minute. They will fill the 96-unit tank in 96/5 minutes, which is 19.2 minutes.

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