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Lesson overview

Number - fractions

Fractions can only be added or subtracted directly when they count the same kind of part. If the denominators do not match, we rename the fractions using a common denominator first.

Same denominator

$\frac{2}{7}$ + $\frac{3}{7}$ = $\frac{5}{7}$ because the sevenths stay as sevenths.

Only the numerators change.

Use a common denominator

$\frac{1}{2}$ + $\frac{1}{4}$ becomes $\frac{2}{4}$ + $\frac{1}{4}$ .

Rename one fraction so both use the same parts.

Subtract after renaming

$\frac{3}{4}$ - $\frac{1}{2}$ becomes $\frac{3}{4}$ - $\frac{2}{4}$ .

Then subtract the numerators.

Worked example

Calculate $\frac{1}{2}$ + $\frac{3}{10}$ .

Use a common denominator of 10.
$\frac{1}{2}$ becomes $\frac{5}{10}$ .
Add the numerators: 5 + 3 = 8.
The answer is $\frac{8}{10}$ , which is also $\frac{4}{5}$ .

Round 1: Learn it

Check whether the denominators already match before you start.

Finish this round to unlock Round 2: Show you know it.

Question 1

What is $\frac{2}{7}$ + $\frac{3}{7}$ ?

Question 2

What is $\frac{1}{2}$ + $\frac{1}{4}$ ?

Question 3

What is $\frac{3}{4}$ - $\frac{1}{2}$ ?

Question 4

What is $\frac{1}{2}$ + $\frac{3}{10}$ ?

Question 5

Which is $\frac{5}{6}$ - $\frac{2}{6}$ ?

Common mistakes

Watch for these as you work through the lesson.

Adding the denominators as well as the numerators.
Choosing a denominator that is not common to both fractions.
Subtracting before renaming to matching parts.

Add and subtract fractions with the same denominator and denominators that are multiples of the same number

Lesson overview

Worked example

Round 1: Learn it

Common mistakes

Related topics

Independent practice will plug in here