-80% is the change from 320 to 64
Calculation steps:
[( 64 - 320 ) ÷ 320] x 100 = -80%
Formula
Percentage change = [(64 - 320) / 320] x 100
Subtract the new number by the original number
64 - 320 = -256
-256 ÷ 320 = -0.8
-0.8 x 100 = -80%
Example