Answer :

well 25x4=100 so 21x4=84 so 84 over 100 is the same as .84 =D hope it helps
AL2006
A fraction means division.  21/25 means  21  divided by  25. 
When you actually do the division, the quotient is the decimal
equivalent of the fraction.

When you divide  21  by  25, you get  0.84 .