Take a look at this site.
http://www.mathsisfun.com/simplifying-fractions.html
google it. Lol.
Kevin Bacon
You have to divide both numerator (the upper number) and denominator (the downer number) by their Highest Common Factor (HCF). If their HCF is 1, you can't reduce : they are called COPRIME numbers.
E.g.
1) \(\frac{7}{21}=\frac{7\div7}{21\div7}=\frac{1}{3}\)
2)\(\frac{108}{216}=\frac{108\div108}{216\div108}=\frac{1}{2}\)
3)\(\frac{45}{150}=\frac{45\div15}{150\div15}=\frac{3}{10}\)
+870 
