What must be true about the denominators of two fractions before you can add them?

The denominators must be the same.

When adding fractions with a common denominator, do you add the denominators as well as the numerators? Explain why or why not.

No, you only add the numerators. The denominator represents the size of the fraction, which doesn't change when adding.

Find the least common multiple (LCM) of the denominators.

Grade 5th Grade · Math · 45 min

I can add and subtract fractions with unlike denominators.

Professor Dave Explains · 4:07

Addition and Subtraction of Fractions

3 key concepts

1
When adding fractions with the same denominator, we only add the numerators and the denominator stays the same.
2
To add fractions with different denominators, we must first find the least common multiple of the denominators.
3
Subtracting fractions is similar to addition, but instead of adding the numerators, we subtract them.

10 questions · Multiple choice & Short answer

Quick comprehension check

“Solve: ⅗ - ¼. Show all steps.”

Get all 3 ready-to-use resources:

Teacher GuideComplete lesson plan

Student DocPrintable student handouts

SlidesReady-to-use presentation