Rakesh can do piece of work in 20 days. How much work can be do in 4 days?

Raj can do a piece of work in 20 days and Rohan can do it in 12 days. How long will they take, if both work together?

Rajan can do a piece of work in 24 days while Amit can do it in 30 days. In how many days can they complete it they work together?

36 men can do a piece of work in 7 days. How many men will do the same work in 42 days ?

A and B together can do a piece of work in 12 days; B and C can do it in 20 days while C and A can do it in 15 days. A, B and C all working together can do it in