X and Y can do a piece of work in 20 days and 12 days respectively. X started the work alone and then after 4 days Y joined him till the completion of the work. How long did the work last?
10 days
Work done by x in 4 days =(120×4)=15
Remaining work =(1−15)=45
(X+Y)’s 1 day’s work = (120+112)=860=215
So,45 work will be done by X and Y in (152×45) = 6 days
Hence, total time taken =(6+4) days=10 days