Question

a and b together can finish a piece of work in 12 days. if a alone can finish the same work in 20 days, in how many days b alone can finish it?

Answer 1

total work --------  12 days 
1 day ------------------- 1/12th part of work can be done
A works 20 days to finish total work
then for 
1day------------------- 1/20th part of work can be done by A alone
1/12=1/20+x
find the value of x
you would get the work done by B in one day
(answer =1/30
B works alone for 30 days)