Think of the original amount as 100%
If we want 100% of something we multiply by 1
To get from 100% to 1, we divide the percentage by 100
Decrease 100% by 19%
100% - 19% = 81%
Then to get the multiplier, divide by 100
81% / 100 = 0.81
To decrease by 19%, multiply by 0.81