Question

A and b can do a piece of work in 12days. b and c can do the same work in 15 days.a and c can do the work in 20 days.a and b and c can do the work in 6 days

Answer 1

(A + B + C)'s 1 day's work =1;6

(A + B)'s 1 day's work =1;8

(B + C)'s 1 day's work =1.12

 (A + C)'s 1 day's work=2 x1-1+16812=1-5324=324=1.8

So, A and C together will do the work in 8 days.

Answer 2

A and B can do a piece of work in 12 days.
A and B can do 1/12 work in 1 day.
B and C can do a work in 15 days.
B and C can do 1/15 work in 1 day.
A and C can do the same work in 20 days
A and C can do 1/20 work in 1 day.
A, B and C can do it in 6 days.
A, B and C can do 1/6 work in 1 day.