-50% is the change from 660 to 330
Calculation steps:
[( 330 - 660 ) ÷ 660] x 100 = -50%
Formula
Percentage change = [(330 - 660) / 660] x 100
Subtract the new number by the original number
330 - 660 = -330
-330 ÷ 660 = -0.5
-0.5 x 100 = -50%
Example