Multiple choice

A tank is fitted with 2 inlet pipes A and B. Both pipes are kept open for 15 minutes to fill 3/5 of the tank and pipe A is closed. If pipe A is thrice as fast as pipe B. How much time will be taken by B alone to complete the remaining work?

  1. 45min

  2. 50 min

  3. 40 min

  4. 30 min

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A is 3 times as fast as B. In 15 mins, they fill 3/5. Rate(A+B) = (3/5) / 15 = 1/25 tank/min. Since A=3B, 4B = 1/25, so B = 1/100 tank/min. Remaining 2/5 tank takes (2/5) / (1/100) = 40 minutes.

AI explanation

Let the time taken by pipe B be x minutes, so pipe A takes x/3 minutes, making their combined hourly rate 3/x + 1/x = 4/x. Using the work formula, working together for 15 minutes they complete 15(4/x) = 3/5 of the tank, which gives x = 100 minutes for pipe B alone. The remaining work is 2/5 of the tank, so pipe B alone needs (2/5) multiplied by 100 minutes to finish. The required time is 40 minutes.

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