-92.19% is the change from 640 to 50
Calculation steps:
[( 50 - 640 ) ÷ 640] x 100 = -92.19%
Formula
Percentage change = [(50 - 640) / 640] x 100
Subtract the new number by the original number
50 - 640 = -590
-590 ÷ 640 = -0.921875
-0.921875 x 100 = -92.19%