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
Number of days required by A and B to finish the work : 12 days
Number of days required by A and B to finish the work : 20 days
Number of days required by A and B to finish the work : 15 days
Work done by A and B in one day: 
Work done by B and C in one day: 
Work done by C and A in one day: 
Work done by (A and B) , (B and C ) and (C and A) in one day that is work done by
(A +B) + (B + C) + (C + A) = 2(A+B+C) = 
Work done by A, B and C = 
= 
They can do the work in 10 days
8