64.4% is the change from 309 to 508
Calculation steps:
[( 508 - 309 ) ÷ 309] x 100 = 64.4%
Formula
Percentage change = [(508 - 309) / 309] x 100
Subtract the new number by the original number
508 - 309 = 199
199 ÷ 309 = 0.6440129449838188
0.6440129449838188 x 100 = 64.4%