-97.19% is the change from 640 to 18
Calculation steps:
[( 18 - 640 ) ÷ 640] x 100 = -97.19%
Formula
Percentage change = [(18 - 640) / 640] x 100
Subtract the new number by the original number
18 - 640 = -622
-622 ÷ 640 = -0.971875
-0.971875 x 100 = -97.19%