Multiple choice

Pipe A can fill an empty tank in 30 hours while B can fill it in 45 hours. Pipe A and B are opened and closed alternatively i.e., first pipe A is opened, then B, again A and then B and so on for 1 hour each time without any time lapse. In how many hours the tank will filled if it was empty initially?

  1. 36

  2. 54

  3. 48

  4. 60

  5. None of these

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A fills 1/30 per hour, B fills 1/45 per hour. In 2 hours (A then B), tank fills by 1/30 + 1/45 = 5/90 = 1/18. After 36 hours (18 cycles), tank fills by 18/18 = 1. Each full cycle takes 2 hours. 36 hours ÷ 2 hours/cycle = 18 complete cycles.