-10% is the change from 300 to 270
Calculation steps:
[( 270 - 300 ) ÷ 300] x 100 = -10%
Formula
Percentage change = [(270 - 300) / 300] x 100
Subtract the new number by the original number
270 - 300 = -30
-30 ÷ 300 = -0.1
-0.1 x 100 = -10%
Example