I can't tell you why; in fact, I can't imagine why you would want to do what you suggest.
Oh, maybe I can see what you want to do...but you can"t!
In order to add or subtract fractions, the fractions must have a common denominator...why that is so is a story too long to tell here, but maybe I can show you what happens when you do what you suggest.
The fraction in this problem could be represented as (a - b)/(c + b) where b represents the 250000 and the other letters represent the other part of the fraction.
[(a - b)(c +b] - 1 means [(a -b)/(c + b)] - (c + b)/(c + b) = (a - b - c - b)/(c + b) which is certainly NOT your original fraction!
The correct way to do this is to evaluate the numerator as 23082 and the denominator as 257330 and then perform the division.
I hope this helps. You clearly need to review the method for addition and subtraction of fractions and why that method is necessary. You also need to understand what the numerator and denominator of a fraction means. Good luck.
