A and B can do a piece of work in 12 days, B and C in 15 days, and C and A in 20 days. How much time will A alone take to finish the job?
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 : 15 days
Number of days required by A and B to finish the work : 20 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 = 
= 
A ‘s one day work = (A +B + C ) ‘s one day work – (B + C) ‘s one day work = 
– 
= 
A alone can complete the work in 30 days.
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