Question

A,B andC working together can finish a work in 3 days. A alone can do it in 6 days and B can do it in 15/2 days. In how many days can C alone finish the same work?

Answer 1

LCM of 20, 30 and 60 is 60

So we will take total work to be 60 units.

A = 60/20 = 3 units/day

B = 60/30 = 2 units/day

C = 60/60 = 1 units/day

Now A is working two days alone and on third day B and C are joining him and this goes on and on until work is done.

Day 1 = A’s work = 3 units

Day 2 = A’s work = 3 units

Day 3 = (A + B +C) ‘ s work = 3 + 2 + 1 = 6 units

So this is a set of 3 days in which total 3+3+6 = 12 units work is being done.

Now to complete 60 units, 60/12 = 5 such sets of 3 days are needed.

5 sets of 3 days means 5*3 = 15 days