Yes, you do.
Yes
You can add or subtract fractions only if they are "like" fractions, that is, only if they have the same denominator - unless you know your fractions really well.
Because addition and subtraction are defined in terms of like terms.
You add or subtract only the numerators
Common Denominator means that the denominators in two (or more) fractions are common, or the same. The common denominator is important because before you can add or subtract fractions, the fractions need to have a common denominator.Sometimes fractions have different denominators, like 2/3 and 3/4. If you want to add or subtract them, they need to have the same denominator. In order to do that, you find a common denominator which is the same thing as a common multiple, only with denominators.
You need to find the common denominator in order to add or subtract them. You can only add or subtract "like things" and by finding a common denominator you make both rational expressions into things that can be added or subtracted.
You DO need a common denominator to add, subtract, or compare fractions. You DO NOT need a common denominator to multiply or divide fractions.
Because it tells you how much the fraction is out of.
Just add the numerators together but the denominator remains the same
They are called like fractions.In order to add or subtract fractions you will usually need to convert them to like fractions. Then you simply add or subtract the numerators (as required) to form the numerator of the answer. The same (or common) denominator is the denominator of the answer. You may need to simplify the resulting fraction.
Unless you are using a calculator that adds them for you, it is much harder to add fractions with uncommon denominators. Having the same denominator allows you to only have to add the numerators for your answer.
They need a common denominator when you add them. For example, if you want to add 1/2 and 1/3, you need to change the fractions to equivalents that share the same denominator, so you can combine them. 1/2 + 1/3 = 3/6 + 2/6 = 5/6