Decomposing Fractions


To decompose means to break apart. Your child has already decomposed whole numbers with number bonds, tape diagrams, and place value charts. In fourth grade, he will decompose fractions.

Three-eighths is a fraction. We can decompose three-eighths into parts using a tape diagram as the visual model. One-eighth, plus one-eighth, plus one-eighth equals three-eighths.Your child will write this as an equation. These are called unit fractions.

He will also decompose three-eighths as two-eighths plus one-eighths. Decomposing fractions into different parts helps your child to understand that one whole can be expressed in more than one way.

Sometimes your child will work with improper fractions. Ten-fourths is an improper fractions because the numerator is greater than the denominator. Your child will decompose an improper fraction by considering the denominator and pulling out one whole. Four-fourths equals one whole. After pulling out four-fourths, six-fourths remain.

But wait! He can pull out another whole! Your child knows one whole equals one, so he can now see ten-fourths equals one plus one plus two-fourths.

Practice decomposing fractions with your child so he will be ready for mixed numbers and performing operations with fractions!

And that’s good to know.

This video addresses Common Core Grade 4 Standard Number & Operations – Fractions: Build fractions from unit fractions by applying and extending previous understandings of operations on whole numbers.

(4.NF.3) Understand a fraction a/b with a greater than 1 as a sum of fractions 1/b.
(4.NF.3b) Decompose a fraction into a sum of fractions with the same denominator in more than one way, recording each decomposition by an equation. Justify decompositions, e.g., by using a visual fraction model. Examples: ⅜ = ⅛ + ⅛ + ⅛ = ⅛ + 2/8; 2 ⅛ = 1 + 1 + ⅛ = 8/8 + 8/8 + ⅛ .