Multiple choice

Pipe C and D can fill a tank in 4 and 5 hours, respectively. If pipe C is closed after 3 hours at the same time pipe D is opened, in how many hours will the tank get filled?

  1. 0.8

  2. 1.25

  3. 1

  4. 1.5
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In 3 hours, pipe C fills 3/4 of the tank (at 1/4 per hour). Remaining 1/4 is filled by pipe D at 1/5 per hour, taking 1/4 × 5 = 1.25 hours. Total fill time is 3 + 1.25 = 4.25 hours from start, but D worked for only 1.25 hours.

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