-1.21% is the change from 825 to 815
Calculation steps:
[( 815 - 825 ) ÷ 825] x 100 = -1.21%
Formula
Percentage change = [(815 - 825) / 825] x 100
Subtract the new number by the original number
815 - 825 = -10
-10 ÷ 825 = -0.012121212121212121
-0.012121212121212121 x 100 = -1.21%