Question

A can do a piece of work in 25 days and B can finish it in 20 days. They work together for 5 days, then A leaves. In how many days will B finish the work??

Answer 1

Think of it this way:

Both of them are doing 5 days of work. They both do some fraction of it.

5/25= A 1/5= 4/20

5/20= B 1/ 5/20

They do 9/20 of the work or 9 days of work.

20-9=11

It will take B 11 days to do the rest of the work.

I hope this helps!
~kaikers

Answer 2

If A can do a piece of work in 25 days, then he can do
`(1)/(25)` of all work per day.

If B can finish work in 20 days, then he can do
`(1)/(20)` of all work per day.

Together per day they can do

`(1)/(25)+(1)/(20)=(4+5)/(100)=(9)/(100)`

of all work.

They work together for 5 days, then the work done after these 5 days is

`5\cdot (9)/(100)=(9)/(20)` of all work.

If then B finishes alone, it is left for him

`1-(9)/(20)=(11)/(20)` of all work.

Since B can do
`(1)/(20)` of all work per day, then
`(11)/(20)` of all work he can do in 11 days.

Answer: B will finish the work in 11 days.