Answer :

Kaikerscupcake
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
frika

If A can do a piece of work in 25 days, then he can do [tex]\dfrac{1}{25}[/tex] of all work per day.

If B can finish work in 20 days, then he can do [tex]\dfrac{1}{20}[/tex] of all work per day.

Together per day they can do

[tex]\dfrac{1}{25}+\dfrac{1}{20}=\dfrac{4+5}{100}=\dfrac{9}{100}[/tex]

of all work.

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

[tex]5\cdot \dfrac{9}{100}=\dfrac{9}{20}[/tex] of all work.

If then B finishes alone, it is left for him

[tex]1-\dfrac{9}{20}=\dfrac{11}{20}[/tex] of all work.

Since B can do [tex]\dfrac{1}{20}[/tex] of all work per day, then [tex]\dfrac{11}{20}[/tex] of all work he can do in 11 days.

Answer: B will finish the work in 11 days.

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