Multiple choice

(\text{Pipe A can fill a tank in 30 hours and pipe B in 45 hours. If both pipes are opened in the same empty tank, how much time will it take to fill it?})

  1. 12 hrs.

  2. 9 hrs.

  3. 18 hrs.

  4. 16 hrs.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Pipe A fills at 1/30 tank per hour. Pipe B fills at 1/45 tank per hour. Combined rate: 1/30 + 1/45 = 3/90 + 2/90 = 5/90 = 1/18 tank per hour. Therefore, time to fill = 18 hours. Alternatively: LCM(30,45) = 90. A fills 3 units, B fills 2 units per hour, total 5 units per hour. 90 units ÷ 5 = 18 hours.

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