Multiple choice general knowledge math & puzzles

Pipe A can fill in 20 minutes and Pipe B in 30 mins and Pipe C can empty the same in 40 mins.If all of them work together, find the time taken to fill the tank

  1. 17 1/7 mins

  2. 20 mins

  3. 8 mins

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Net rate per minute = 1/20 + 1/30 - 1/40. Common denominator is 120. Rate = (6 + 4 - 3) / 120 = 7 / 120. Time taken = 120 / 7 = 17 1/7 minutes.

AI explanation

To solve this question, we can use the concept of the rate of work.

Let's say that the capacity of the tank is 1 unit.

Pipe A can fill the tank in 20 minutes, which means it can fill 1/20 of the tank in 1 minute.

Pipe B can fill the tank in 30 minutes, which means it can fill 1/30 of the tank in 1 minute.

Pipe C can empty the tank in 40 minutes, which means it can empty 1/40 of the tank in 1 minute.

When all three pipes work together, the net rate of work will be the sum of their individual rates.

So, the net rate of work = (1/20 + 1/30 - 1/40) tank per minute

To find the time taken to fill the tank, we can use the formula:

Time = 1 / (Net rate of work)

Time = 1 / (1/20 + 1/30 - 1/40)

Simplifying this expression, we get:

Time = 17 1/7 minutes

Therefore, the correct answer is option A) 17 1/7 minutes.

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