So you divide 200 by 100 so 210/100, thats when you get 2.1. So to convert that from percent to decimal all you do is is just divide by 100 and remove the % sign! Just move the decimal point 2 places to the left. If the percent value is a integer, the '.' is at the right of the right most digit.
Hope this helped you out and hope you got your answer right! Enjoy the rest of your day. :)