Question 130705
Let x= amount of time it will take B to finish the job
A works at the rate of 1/25 of the job per day
B works at the rate of 1/20 of the job per day

Together A & B work at the rate of 1/25  +  1/20=
4/100 + 5/100= 9/100 of the job per day

If they both work together for 5 days, they complete (9/100)*5 or 
45/100 of the job, leaving 55/100 of the job yet to be done

B can do 1/20 of the job per day, so:

(1/20)*x=55/100  multiply each side by 100
5x=55  divide both sides by 5
x=11 days-----------------amount of time needed by B to finish the job


Hope this helps---ptaylor