Multiple choice

Water from a tank moves through a pipe to fill a swimming pool. Pipes P and Q can fill a cylindrical tank in 24 min and 32 min, respectively. Both pipes are opened. After what time should pipe Q be closed, so that the tank is full in 18 minutes?

  1. 8 minutes

  2. 9 minutes

  3. 6 minutes

  4. 10 minutes

  5. 11 minutes
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let Q be closed after x minutes. Pipe P works for 18 minutes, filling 18/24 = 3/4 of the tank. Pipe Q works for x minutes, filling x/32 of the tank. 3/4 + x/32 = 1 implies x/32 = 1/4, so x = 8.

AI explanation

Using the least common multiple method, let the total tank capacity be 96 units. Pipe P fills at 4 units per minute and pipe Q fills at 3 units per minute. Pipe P runs for the entire 18 minutes, filling 72 units, which leaves 24 units to be filled by pipe Q. The time pipe Q needs to be open is 24 divided by 3, resulting in 8 minutes.

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