A & B undertake to do a piece of work for Rs. 100. A can do it in 5 days & B can do it in 10days. With the help of C, they finish it in 2 days. How much should C be paid for his contribution?

40??

If correct let work be 10units to be completed in 2days ,in 1 day 5units of work A can do 2units and B can do 1 units of work in a day therefore c should 2 units of work in a day(since 2+1+2=5units in a day).therefore ratio of efficiencies of A,B,C is 2:1:2 and get paid 100 => A=40,B=20 and C= 40

A-40, B-20, C-40