-67.34% is the change from 640 to 209
Calculation steps:
[( 209 - 640 ) ÷ 640] x 100 = -67.34%
Formula
Percentage change = [(209 - 640) / 640] x 100
Subtract the new number by the original number
209 - 640 = -431
-431 ÷ 640 = -0.6734375
-0.6734375 x 100 = -67.34%