Question

A and B can do a piece of work in 15 days; B and C can do it in 12 days while C and A can finish it in 20 days. In how many days will A,B,C finish it working together?

Answer 1

a ,b one day work = 1/15
b,c one day work = 1/12
c,a one day work = 1/20
2(a+b+c) one day work
a+b+c one day work = 1/15+1/12+1/20 = 1/5
a+b+c one day work = 1/5×1/2 = 1/10
a one day work = 1/10 - 1/12 = 1/60
= 60days
b one day work = 1/10 - 1/20 = 1/20
= 20days
c one day work = 1/10 - 1/15 =1/30
= 30 days