Multiple choice

A water tank is one-sixth full. There are two pipes L and M. L can fill the tank in 6 minutes and M can empty it in 4 minutes. Find the time it takes to empty the tank, if both pipes are opened.

  1. 2 minutes

  2. 4 minutes

  3. 8 minutes

  4. 12 minutes

  5. 9 minutes
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let the tank capacity be 12 units. Pipe L fills 2 units/min, and pipe M empties 3 units/min. The net rate is -1 unit/min. Since the tank is 1/6 full (2 units), it takes 2/1 = 2 minutes to empty.

AI explanation

Using the LCM method, let the total capacity of the tank be 12 units. Since the tank is one-sixth full, it currently holds 2 units of water. Pipe L fills at 2 units per minute and pipe M empties at 3 units per minute, so their combined rate is a net emptying rate of 1 unit per minute. To empty the 2 units of water currently in the tank, it takes 2 divided by 1, which equals 2 minutes.

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