Plus and Minus (Equal Denominators)

When adding or subtracting fractions with equal denominators, add or subtract the numerators and keep the denominator as it is.

Rule

\frac{a}{c} + \frac{b}{c} = \frac{a + b}{c}, c \neq 0

Rule

\frac{a}{c} - \frac{b}{c} = \frac{a - b}{c}, c \neq 0

Example 1

Compute $\frac{1}{4} + \frac{2}{4}$ and $\frac{4}{6} - \frac{3}{6}$

Using the rule above, you get that

\frac{1}{4} + \frac{2}{4} = \frac{1 + 2}{4} = \frac{3}{4} .

The same goes for subtraction, only now you have to subtract:

\frac{4}{6} - \frac{3}{6} = \frac{4 - 3}{6} = \frac{1}{6} .

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An Important Trick

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Activities 3