Adding and Subtracting Fractions

Grade 4 · Math · Study Guide

Learn how to add and subtract fractions that have the same denominator.

A fraction shows part of a whole. The bottom number (denominator) tells you how many equal parts the whole is divided into. The top number (numerator) tells you how many of those parts you have. When fractions have the same denominator, adding or subtracting them is straightforward — just add or subtract the numerators and keep the denominator the same.

For example, 2/8 + 3/8 = 5/8. Picture a pizza cut into 8 slices: if you eat 2 slices and your friend eats 3 more, together you ate 5 out of 8 slices. The pizza is still cut into 8 pieces — the denominator doesn't change!

Subtraction works the same way. 7/10 − 3/10 = 4/10. You start with 7 out of 10 pieces, take away 3, and you're left with 4. Always simplify your answer if possible: 4/10 simplifies to 2/5 because both 4 and 10 can be divided by 2.

In 4th grade you also add and subtract fractions on a number line. Mark your starting point, then jump forward or backward by the amount of the second fraction. This visual approach helps you see exactly what's happening!

Key terms

Numerator

The top number in a fraction — it tells how many parts you have.

Denominator

The bottom number in a fraction — it tells how many equal parts in the whole.

Like fractions

Fractions that share the same denominator.

Simplify

Rewrite a fraction in lowest terms by dividing numerator and denominator by their greatest common factor.

Flashcards

Numerator

The top number of a fraction; tells how many parts are counted.

Denominator

The bottom number of a fraction; tells the total number of equal parts.

3/7 + 2/7

5/7 — add numerators, keep the denominator.

9/10 − 4/10

5/10 = 1/2 simplified

Like fractions rule

Add or subtract the numerators only. Keep the denominator the same.

Simplify 4/8

1/2 — divide both numerator and denominator by 4.

Practice questions

1. What is 3/8 + 4/8?

   1. 7/16
   2. 7/8
   3. 1/2
   4. 3/4
   Show answer

   Answer: 7/8

   3/8 + 4/8: same denominator, so add numerators: 3 + 4 = 7. Answer is 7/8.

2. When adding fractions with the same denominator, you add the denominators together.

   Show answer

   Answer: False

   When adding like fractions, you keep the denominator the same and add only the numerators.

3. 5/9 − 2/9 = ___

   Show answer

   Answer: 3/9

   5/9 − 2/9: subtract numerators: 5 − 2 = 3. Keep denominator: 3/9 (also equals 1/3 simplified).

4. Which fraction equals 6/10 − 2/10 simplified?

   1. 4/5
   2. 2/5
   3. 4/10
   4. 8/10
   Show answer

   Answer: 2/5

   6/10 − 2/10 = 4/10. Simplify 4/10 by dividing both by 2: 2/5.

5. 1/6 + 4/6 = ___

   Show answer

   Answer: 5/6

   1/6 + 4/6: add numerators: 1 + 4 = 5. Keep denominator 6. Answer: 5/6.

Fun facts

• Ancient Egyptians only used fractions with a numerator of 1 — like 1/2 or 1/7. They'd write 3/4 as 1/2 + 1/4!
• The fraction bar you see between numerator and denominator is called a vinculum.

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