In order to add or subtract fractions, they must have the same denominator.
For a set to be closed under any operation, the result of the operation must also be a member of the set. The result of adding fractions is another fraction, thus it is closed under addition. Remember that 8/3, 8/4, 4/4, 2/1 are all fractions - they have a numerator and denominator separated by a line (at an oblique angle on the computer screen). Improper fractions are still fractions.
The usual rules of addition of fractions apply.
Addition or subtraction of fractions require "like" fractions: that is, fractions with the same denominator.
The answer to an addition is called the sum. Fractions and other numbers.
For addition, subtraction, division and multiplication with other fractions
You look for a common denominator; convert the fractions to equivalent fractions with the denominator you found; then you do the addition itself.
Blueprint reading, addition, fractions,
Similar fractions are fractions with the same denominator. In order to add or subtract fractions they need to be similar.