You should know that you may perform the addition of two fractions having like denominators or the fractions may have different denominator.

When the denominators are the same, you'll add only the numerators of the fraction.

1/2 + 4/2 = (1+4)/2 = 5/2

When the denominators are different, you need to bring these fractions to a common denominator.

You need first to calculate the least common denominator of each denominator of fraction. Then, you need to determine the least common denominator of the fractions.

1/2 + 1/6 = 1/2 + 1/(2*3)

You notice that the leasct common denominator of the farctions is 6.

Multiplying by 3 the first fraction yields:

3/6 + 1/6

Since the fractions have the same denominator, you will add only the numerators such that:

3/6 + 1/6 = (3+1)/6 = 4/6 = 2*2/2*3

Reducing by 2 yields:

3/6 + 1/6 = 2/3

The subtraction of fractions implies the same rules as addition.