Question

Pipe A can fill an empty cistern in 4 hours while along with pipe B it can fill it up in 3 hours.Only pipe A is turned on for an hour after which pipe B is also turned on.How much total time will it take to fill up the cistern?​

Answer 1

Answer:

1 hour 15 minutes

Explanation:

Given : Pipe A can fill an empty cistern in 4 hours while along with pipe B it can fill it up in 3 hours.Only pipe A is turned on for an hour after which pipe B is also turned on.

To find : when only pipe A is turned on for an hour after which pipe B is also turned on. Time taken to fill cistern

Solution :

Pipe A can fill the cistern in 4 hours

In 1 hour = 1/4 of the cistern can be filled

Pipe B can find the cistern in 3 hours

In 1 hour = 1/3 of the cistern can be filled

If both combined together,

In 1 hour = 1/4 + 1/3 = 1(3)/12 + 1(4)/12 = 3/12 + 4/12 = 7/12 of the cistern can be filled.

Find amount of work left after 1 hours

work left = 1 - 7/12 = 12/12 - 7/12 = 5/12 of the cistern can be done

Find the amount of time needed for B to finish the rest of the work:

In 1 hour = 1/3 of the cistern can be filled

Number of hours needed = 5/12 ÷ 1/3

= 5/12 * 3

= 5/4

=> 1 1/4 hours=  1 hours (1/4 * 60)

= 1 hour 15 minutes

It will take 1 hours 15 minutes for Pipe B to fill the remaining of cistern.