Proper, Reduced Fractions
Reducing a fraction to its lowest terms (also known as an Irreducible Fraction) requires that the numerator and denominator are divided by their Greatest Common Divisor.
It can be simpler to expand the numerator and denominator into their Prime Factors and then eliminate all common terms.
For example, to reduce the following Fraction
30  =  2 x 3 x 5  = 

=  5 
42  2 x 3 x 7 

7 
The common factors are 2 x 3, which means the numerator and denominator can be divided by the Greatest Common Divisor of 6 to give the final answer of 5/7