-40.59% is the change from 850 to 505
Calculation steps:
[( 505 - 850 ) ÷ 850] x 100 = -40.59%
Formula
Percentage change = [(505 - 850) / 850] x 100
Subtract the new number by the original number
505 - 850 = -345
-345 ÷ 850 = -0.40588235294117647
-0.40588235294117647 x 100 = -40.59%