A fraction that is equivalent to [tex]\frac{a}{b}[/tex] will have the form [tex]\frac{a\times A}{b\times B}[/tex], where A and B are equivalent and factors that are multiplied in.
The product fraction should be easily simplified using A and B to get the original fraction.
In the case of your fraction [tex]\frac{7}{10}[/tex] you will need to find a fraction which is a product of this: [tex]\frac{7\timesA}{10\timesB},A=B[/tex]