A can complete a task in 15 days and B in 10 days. They work together for 2 days and then B leaves. A day later ‘C joins ‘A’ and the task is completed in the next 3 days. How long will ‘C take to complete the task if she worked alone?

Explanation:

In 2 days, A and B will finish 2\15+2\10=4+6\30=1\3th of the work

In another day, A can do 1\15th of the work

Therefore, total work completed = 1\3+1\15=5+1\15=2\5th of the work.

Remaining 3\5th of the work will be completed by A and C in 3 days

Therefore, 3\5 = 3\15+3\x or x = 7.5 days

So, C will take 7.5 days to complete the work if he works alone.