Your equation would be correct if you would place 
parentheses correctly. This is your reasoning,
using 

  


Not this:

100/x - 2.5 = 100/x+2

But this:

100/x - 2.5 = 100/(x+2)

When typing algebra all on 1 line, if a
numerator or a denominator contains more
than just 1 number, or just 1 letter, you
must type a left parenthesis "(" to indicate
where the numerator or denominator starts,
and a right parenthesis ")" to indicate where
it ends.

Edwin