-39.88% is the change from 840 to 505
Calculation steps:
[( 505 - 840 ) ÷ 840] x 100 = -39.88%
Formula
Percentage change = [(505 - 840) / 840] x 100
Subtract the new number by the original number
505 - 840 = -335
-335 ÷ 840 = -0.39880952380952384
-0.39880952380952384 x 100 = -39.88%