Decomposing Fractions

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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 .

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