Section 03 · Addition and Subtraction · F09

Subtracting fractions with like denominators

I can subtract fractions with the same denominator and find how much is left or how far apart two amounts are.

Learn

There is 7/8 of a pizza left and you eat 3/8. How much remains?

Subtracting like fractions means taking away same-sized parts. Subtract the numerators; keep the denominator.

7/8 − 3/8 = 4/8, which simplifies to 1/2.

To subtract from a whole number, rewrite the whole with the same denominator: 1 − 3/8 = 8/8 − 3/8 = 5/8.

With mixed numbers, convert to improper fractions if the fraction part is too small: 2 1/5 − 4/5 = 11/5 − 4/5 = 7/5.

Start at 7/8 and press the numerator − button 3 times. You are subtracting 3/8 one slice at a time.

Fraction circles showing 7 eighths: 1 circle, each cut into 8 equal slices, with 7 shaded.

Numerator7

Denominator8

Use the hints as much as you like. You can try each question as many times as you need.

0 of 2 solved

5/6 − 1/6 = ? (any equivalent form)

1 − 3/8 = ?

Answers are checked exactly — equivalent fractions count unless a question asks for a particular form.

0 of 4 solved

7/4 − 3/4 = ?

2 1/5 − 4/5 = ? (any form)

A ribbon is 9/10 m long. You cut off 4/10 m. How long is the rest, in simplest form?

How much greater is 11/12 than 5/12? Simplest form.

Subtracting denominators: 5/6 − 1/6 = 4/0.

Why it happens: The parts stay sixths. A zero denominator is meaningless.

What to do: Keep the unit and subtract only the count of parts.

Treating 1 as 1/8 when subtracting 3/8.

Why it happens: One whole contains all 8 eighths.

What to do: Rename the whole using the same denominator before subtracting.

Three practice questions to check your understanding. Hints and retries are allowed, so this counts as practice — not mastery.

0 of 3 solved

8/9 − 2/9 in simplest form.

2 − 5/6 = ? (any form)

3 3/4 − 1 1/4 = ? Write as a mixed number.

Ready? Answer 4 new questions with no hints and one try each. This is the only way a lesson is marked as mastered.