Question

pipe A can fill a cistern in 36 minutes and B in 48 minutes.if both the pipes are opened together,when should pipe B be closed so that the cistern may be just full in 24 minutes​

Answer 1

Answer:

18 min

Step-by-step explanation:

solve.

(1/36+1/48)x +(1/48)24-x=1

so, here x is time taken by A and B together

so time when B must close is first 18 min

please check this

may it will be helpfull

Answer 2

Given:

A can fill it in 36 mins

B can fill it in 48 mins

To Find:

When should B be closed so that they it takes 24 mins to fill.

Solution

A can fill it in 36 mins

$\implies \text{1 min } = \dfrac{1}{36}$

B can fill it in 48 mins

$\implies \text{1 min } = \dfrac{1}{48}$

Together:

$\text{1 min } = \dfrac{1}{36} + \dfrac{1}{48}$

$\text{1 min } = \dfrac{7}{144}$

Define x:

Total time to fill the cistern = 24 mins

Let x be the number of minutes that they should both be open.

Therefore (24 - x) is the number of minute that pipe B is closed.

Solve x:

$\dfrac{7}{144} x + \dfrac{7}{36} ( 24 - x) = 1$

$\dfrac{7x}{144} + \dfrac{2}{3} - \dfrac{x}{36} = 1$

$\dfrac{7x}{144} - \dfrac{x}{36} = 1 - \dfrac{2}{3}$

$\dfrac{1x}{48} = \dfrac{1}{3}$

$3x = 48$

$x = 16$

Find the time:

Time to keep both open = x

Time to keep both open = 16 mins

Answer: Pipe B should be closed after 16 mins