A can do a job in 16 days, and B can do the same job in 12 days. With the help of C, they did the job in 4 days only. In how many days can C do the job alone?
Answer: A
Work done by (A+B+C) in 1 day = 1/4. Work done by A in 1 day = 1/16. Work done by B in 1 day = 1/12. Work done by C in 1 day = \(1/4 - (1/16 + 1/12) = 1/4 - (3+4)/48 = 1/4 - 7/48 = (12-7)/48 = 5/48\). So, C alone can do the work in 48/5 = 9.6 days.