-2.91% is the change from 688 to 668
Calculation steps:
[( 668 - 688 ) ÷ 688] x 100 = -2.91%
Formula
Percentage change = [(668 - 688) / 688] x 100
Subtract the new number by the original number
668 - 688 = -20
-20 ÷ 688 = -0.029069767441860465
-0.029069767441860465 x 100 = -2.91%