Answer :
A = old value
B = new value
C = percent change
C = [ (B-A)/A ] * 100%
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Example:
Lets say we start at A = 10 and increase to B = 15. The percent change would be...
C = [ (B-A)/A ] * 100%
C = [ (15 - 10)/10] * 100%
C = (5/10) * 100%
C = 0.5 * 100%
C = 50%
The positive C value means we have a percent increase. Going from 10 to 15 is a 50% increase.