-49.38% is the change from 640 to 324
Calculation steps:
[( 324 - 640 ) ÷ 640] x 100 = -49.38%
Formula
Percentage change = [(324 - 640) / 640] x 100
Subtract the new number by the original number
324 - 640 = -316
-316 ÷ 640 = -0.49375
-0.49375 x 100 = -49.38%