At furnace woods school, enrollment increased from 320 students in 2006 to 349 students in 2007. what is the percent increase in enrollment? let me know how to do it without the computer calculations so i can do problems like these on my own

Here are two slightly different ways to look at it. 
Both ways do exactly the same thing.

Way #1:
Divide  (the new number) by (the old number)

 349 / 320 = 1.090625

Change the quotient  1.090625  to percent.

To change any number into percent, multiply it by 100, or move the decimal point  2 places to the right.

   1.090625  ==>  109.06 %

The new number  (349)  is  109.06%  of the old number  (320).

But the old number was  100%  of itself.  So the new number
is  9.06%  more than the old number was.


Way #2:
How much bigger is the new number ?

       (349 - 320) = 29 bigger

Divide the increase by the old number:

       29 / 320 = 0.090625

Change the quotient to a percent.

     0.090625 = 9.06%

The increase is  9.06%  of the old number.