A and B working separately can do a piece of work in 9 and 15 days respectively. If they work for a day alternately, with A beginning, then the work will be complete in :

[A]9 days

[B]10 days

[C]11 days

[D]12 days

**11 days**

A’s 1 day’s work

B’s 1 day’s work

Work done in first 2 days = A’s 1 day’s work + B’s 1 day’s work

∴ Work done in first 10 days

Remaining work

Now it is turn of ‘A’ for the eleventh day.

∴ Time taken by ‘A’ in doing work

Hence option [C] is correct answer.