(c) Let (c) completes the work in x days. Work done by ((a) + (b)) in 1 day =
1
10
Work done by ((b) +(c)) in 1 day =
1
18
(a)’s 5 days’ work + (b)’s 10 days’ work +(c)’s 15 days’ work = 1 or ((a) + (b))’s 5 days’ work + ((b) + (c))’s 5days’ work + (c)’s 10 days’ work = 1 or