It can take 12 hours to fill a swimming pool using two pipes. If the pipe of larger diameter is used for 4 hours and the pipe of smaller diameter for 9 hours, only half of the pool can be filled. How long would it take for each pipe to fill the pool separately?

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A = 20, B = 30

A = 40, B = 34

A = 20, B = 50

A = 12, B = 23

answer is A.

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Detailed Solution

Concept- For solving this question we will consider time taken from pipes of larger and smaller diameter as variables and make an equation as the given conditions. There should be a maximum of 2 equations ,since we have to find the time of two pipes of different diameter. Doing this will give you correct answer.Let the time taken by the first pipe be

hours and the time taken by the second pipe be y hours.
in 1 hour the first pipe can fill it

in 1 hour the second pipe can fill it

(1)

Consider

and

……..(3)

……….(4)
Multiplying equation (3) by 4 , we get,

Now, Equation (4) - (5)

Substituting the value of y in equation in (3) we get

So, the first pipe would take 20 hours and the second pipe would take 30 hours.
Hence, option is 1 is correct.

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