-23.44% is the change from 640 to 490
Calculation steps:
[( 490 - 640 ) ÷ 640] x 100 = -23.44%
Formula
Percentage change = [(490 - 640) / 640] x 100
Subtract the new number by the original number
490 - 640 = -150
-150 ÷ 640 = -0.234375
-0.234375 x 100 = -23.44%