why do we have to multiply and divide fractions to get percent or decimals?

because its the same thing      fractions are just a way to represent part of a whole   3/4 is 3 out of 4    or 3 /  4 which is 75.00 percent   75/100     percent just means of a hundred  

a good way to think about it is  in terms of money   100% is 1/1 or a dollar   if you have 75%   you would have .75  cents  not a whole dollar yet