Question

a man can do a piece of work in 5 days . he and his son working together can finish it in 3 days . in how many days can the son do it alone ?

Answer 1

The man can do 1/9 (or 4/36) of the job per day and there's 11/36 of the job left
So it will take the man working alone (11/36)/(4/36) days to finish
(11/36)/(4/36)=(11/36)(36/4)=11/4 =2.75 days
So it will take the man working alone 2.75 days to finish
Hope this helps you !!

Answer 2

one day work M=1/5
together work =1/3
son one day work =1/3-1/5=2/15
son can do the same work in 7.5 days