"Change" is subtracting one value from another.
Example: You had 5 books, but now have 7. The change is: 7-5 = 2.
"Percentage change" represents that value as a percent of the old value ... So divide by the old value and make it a percentage:
So the percentage change from 5 to 7 is: 2/5 = 0.4 = 40%
