I am going to assume you want multiplying and dividing fractions.
When multiplying or dividing fractions there is no need to have the denominators the same, they can be the same or not, it doesn't matter.
When you multiply two fractions the answer is the numerator times the numerator over the denominator times the denominator.
Like this:
When you divide fractions you must invert the divisor and the multiply:
Like this:
More information
here.