Yes inasmuch that the denominators of the fractions must be common to each other.
When multiplying fractions, the numerators (top numbers) are multiplied together and put as the numerator over the denominators (bottom numbers) multiplied together.When adding fractions, they must both have the same denominator - the fractions are made into equivalent fractions with a common denominator; then the numerators are added together and put over the same common denominator.In both cases of multiplication and addition, the resulting fractions are reduced to simplest form.
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The Least (or Lowest) Common Multiple (LCM) is the smallest number that is a multiple of both numbers. For example: the LCM of 10 and 4 is 20, because both 10 and 4 go into 20 and 20 is the smallest number both 10 and 4 can go into. To be able to add or subtract fractions they must have the same denominator. If the denominators are different then the fractions must first be converted into equivalent fractions with a common denominator; any common denominator can be used, but by using the Least Common Multiple of the denominators as the new denominator it keeps the numbers smaller; this smallest denominator is known as the Least Common Denominator Thus the Least Common Denominator is the Least Common Multiple of the denominators of two (or more) fractions (used when adding or subtracting fractions with different denominators). As the Least Common Multiple is used most often with adding or subtracting fractions, it is often referred to as the Least Common Denominator (because the numbers being considered are usually denominators of fractions).
Yes, 'fractions' with different numerators can be added, but not with different denominators. In the case where you have different denominators, you must find the LCM (lowest common multiple).
When adding or subtracting fractions their denominators must be the same
I learned to always change the denominators before adding or subtracting the numerators. You must always have a common denominator before adding or subtracting.
Yes, you must.
Find the lowest common denominator
A Common Denominator
you must make the fractions equivalent and with the same denomenator
you have to find the common factor of the two number befor adding them.
Similarities: the sum does not depend on which number you start with (distributive)Differences: you must find a common denominator for the fractions (whole numbers have a common denominator 
You can only add like to like. There is no mechanism for adding different types of fraction.
When adding or subtracting fractions with different denominators you must find their LCD and this done by finding their LCM