-77.5% is the change from 400 to 90
Calculation steps:
[( 90 - 400 ) ÷ 400] x 100 = -77.5%
Formula
Percentage change = [(90 - 400) / 400] x 100
Subtract the new number by the original number
90 - 400 = -310
-310 ÷ 400 = -0.775
-0.775 x 100 = -77.5%
Example