One pipe fills in 4 hours, another empties in 5. Net fill time = ?
Correct answer: B. 20 hrs
- A. 10 hrs
- B. 20 hrs
- C. 12 hrs
- D. 8 hrs
Explanation
To find the net fill time, calculate the rates of the pipes. The first pipe fills the tank at a rate of 1/4 of the tank per hour. The second pipe empties the tank at a rate of 1/5 of the tank per hour. The net rate of filling is 1/4 - 1/5 = 1/20 of the tank per hour. Therefore, the net fill time for the tank is 20 hours.Option A (10 hrs) assumes an incorrect net rate. Option C (12 hrs) does not align with the correct net rate calculation. Option D (8 hrs) is too short for the given system, not considering the emptying rate properly.
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