Question { Infosys, 42200 }

A and B can finish a piece of work in 20 days .B and C in
30 days and C and A in 40 days.
In how many days will A alone finish the job?

Answer

(A+B)'s 1 day's work = 1/20
(B+C)'s 1 day's work = 1/30
(C+A)'s 1 day's work = 1/40

Adding above, 2(A+B+C)=(1/20)+(1/30)+(1/40)

=13/120
A+B+C =13/240
To get A's work,(A+B+C)-(B+C)=(13/240)-(1/30)
=5/240

Therefore A can finishes the work in 240/5 days .ie 48 days