Simple Averages

Need help sir/maam.

I do have a data with age. N= 10
Age----Count
5------3
10-----2
15-----5

How to compute the averages of a count? (formula) (Nod)
Average shld be = 11

5 + 5 + 5 (<--- 3 times) + 10 + 10 (<-- 2 times) + 15 + 15 + 15 + 15 + 15 (<-- 5 times) = 110
110/10 = 11

Is there any other way? I do have a large set of data (age) And I need a simple formula..

There might be... it's been a while since I've had to learn such things.
Rather than having ___ + ___ + ___ + ___ + ...
you could multiply (using your numbers) 5*3 + 10*2 + 15*5

A simpler way: