Question

A and B can do a piece of work in 12 days,B and C in 13 days,C and A in 20 days.How long would A take separately to do the same work?

Answer 1

A+B = 12 

B+C = 15

A+C = 20

Lcm of (12,15,20) = 60

Efficiency is 

A+B = 5 

B+C = 4

A+C = 3

Total efficiency

2 (A+B+C) = 12 

A+B+C = 6

Individual efficiency

A = 6 - 4 = 2 

B = 6 - 3 = 3 

C = 6 - 5 = 1

Individual time taken

A = 60/2 = 30 days

B =60/3 = 20 days 

C = 60/1 = 60 days