Multiple choice

Two pipes A and B can fill a tank in 4 hours and 5 hours respectively If the pipes A and B are turned on alternately for 1 hour each then what is the time taken to fill the tank ?

  1. $\displaystyle 2\frac{2}{5}$ hours
  2. $\displaystyle 3\frac{2}{5}$ hours
  3. $\displaystyle 4\frac{2}{5}$ hours
  4. $\displaystyle 5\frac{2}{5}$ hours
Reveal answer Fill a bubble to check yourself
C Correct answer
AI explanation

Pipe A fills 1/4 of the tank per hour and pipe B fills 1/5 per hour, so in the first two hours they fill 1/4 + 1/5 = 9/20 of the tank. After two such cycles of two hours, 18/20 is filled, leaving 1/20 empty, which pipe A fills in (1/20) / (1/4) = 1/5 hour. The total time is therefore 4 1/5 hours.

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