first, what was the original number?
it was 200+400=1000!
and when we want to know the change in percent, we divide the "new" number over the "original" number: and we'll know that percentage of the original the new number is!:
\(\frac{200}{1000} *100%= \frac{2}{10} *100%=\frac{200}{10} %=20%.\)
so the percent change was 80 %: the original number was reduced by (100-20)=80 %
