-59.84% is the change from 640 to 257
Calculation steps:
[( 257 - 640 ) ÷ 640] x 100 = -59.84%
Formula
Percentage change = [(257 - 640) / 640] x 100
Subtract the new number by the original number
257 - 640 = -383
-383 ÷ 640 = -0.5984375
-0.5984375 x 100 = -59.84%