-90.63% is the change from 320 to 30
Calculation steps:
[( 30 - 320 ) ÷ 320] x 100 = -90.63%
Formula
Percentage change = [(30 - 320) / 320] x 100
Subtract the new number by the original number
30 - 320 = -290
-290 ÷ 320 = -0.90625
-0.90625 x 100 = -90.63%