Fractions in the formare $$\frac{a}{b}$$ created such that $$a$$ and $$b$$ are positive integers and $$a+b= 425$$. How many such fractions are there which are less than $$1$$ and which cannot be simplified further (that is to say, $$a$$ and $$b$$ have no common factors others than $$1$$)? 
Overseas Competition->Knowledge Point->Number Theory Modules->Factors and Multiples->Common Factors and Common Multiples