Multiple choice

Two pipes can fill a tank in 20 minutes and 24 minutes, respectively. A waste pipe can empty it at the rate of 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is

  1. 60 gallons

  2. 120 gallons

  3. 180 gallons

  4. 240 gallons
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the capacity be C. Rates are C/20, C/24, and -3. Together, C/20 + C/24 - 3 = C/15. Multiplying by 120: 6C + 5C - 360 = 8C, so 3C = 360, C = 120.

AI explanation

Using the LCM method, assume the capacity of the tank is 120 units, making the rates of the two filling pipes 6 units per minute and 5 units per minute. Working together with the waste pipe, their combined rate is 8 units per minute, meaning the waste pipe empties at 3 units per minute. Since the waste pipe empties at 3 gallons per minute, 1 unit equals 1 gallon. Therefore, the total capacity of the tank is 120 gallons.

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