A can do a piece of work in 24 days, while B can do it in 30 days. With the help of C they can finish the whole work in 12 days.How much time is required for C to complete the work, alone?

Efficiency of A = 100/24 = 4.16%
Efficiency of B = 100/30 = 3.33%
Efficiency of (A+ B+C) =100/12 = 8.33%
∴ Efficiency of C = (8.33) - (4.16 + 3.33) = 0.83%
∴ Number of days required by C to complete the work alone
= 100/0.83 = 100/(5/6) = 120 days
(Note : 5/6 = 0.833)