A takes 9 days to complete a task. B will take 12 days and C will take 18 days to complete the same task. All three of them start working on the task and A leaves at the end of day 1. B leaves three days before the task is complete and C is left to complete it. How long will they take to complete the task?

Explanation:

In a day, A will complete 1\9th of the task.

A leaves at the end of day 1.

B and C continue to work it and B leaves 3 days before the task is completed.

So, B and C together would have to complete the remaining 8\9th of the task.

If the task is completed in T days from the start, then B has worked on it for (T – 3) days, while C has worked on it for T days.

Therefore, T−3\12+T\18=8\9

Solving for T, we get 3 (T- 3) + 2T = 32 or 5T = 41 or T = 8.2 days.