Multiple choice

Pipe A took 5 min more than (A+B) to fill a tank. Pipe B took 20 min more than (A+B) to fill the tank. If they both opened together then after how many minutes tank will fill?

  1. 7

  2. 8

  3. 9

  4. 10

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

Let (A+B) together take x minutes. Then A takes x+5 minutes, B takes x+20 minutes. Work rates: 1/(x+5) + 1/(x+20) = 1/x. Solving: (2x+25)/((x+5)(x+20)) = 1/x. Cross multiply: x(2x+25) = (x+5)(x+20). 2x² + 25x = x² + 25x + 100. x² = 100, x = 10. Together they fill in 10 minutes.

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