-60% is the change from 850 to 340
Calculation steps:
[( 340 - 850 ) ÷ 850] x 100 = -60%
Formula
Percentage change = [(340 - 850) / 850] x 100
Subtract the new number by the original number
340 - 850 = -510
-510 ÷ 850 = -0.6
-0.6 x 100 = -60%
Example