Question

a and b can finish a piece of work in 30 days b and c in 40 days while c and a in 60 days how long will they take to finish together

Answer 1

(A+B)'s 1 day work=1/30
(B+C)'s 1 day work=1/40
(C+A)'s 1 day work=1/60
(A+B)+(B+C)+(C+A)'s 1 day work =1/30+1/40+1/60
2(A+B+C)'s 1 day work=4+3+2/120
2(A+B+C)'s 1 day work=9/120
(A+B+C)'s 1 day work=9/120×2
(A+B+C)'s 1 day work=3/80
Hence A+B+C can together do in 80/3days