Basic Math

Understand fraction multiplication | Fifth Grade

Understand Fraction Multiplication | Fifth Grade

Complete Notes & Formulas

1. Multiply Fractions by Whole Numbers: Choose the Model

Definition: When multiplying a fraction by a whole number, we can use different visual models to represent repeated addition of the fraction.

📝 Types of Models:

  • Area Model: Rectangles divided into parts
  • Number Line Model: Showing jumps along a line
  • Set Model: Groups of objects
  • Circle/Fraction Bar Model: Visual fractions
  • Array Model: Rows and columns

🔑 Key Concept:

4 × 2/3 means "4 groups of 2/3"

2. Multiply Fractions by Whole Numbers Using Models: Complete the Equation

Definition: Use visual models to find the product and complete multiplication equations.

📝 Steps to Complete Equation:

  1. Look at the model shown
  2. Count how many groups are shaded
  3. Count total shaded parts (numerator)
  4. Identify the denominator (parts in each whole)
  5. Write as a fraction or mixed number

✏️ Example: 3 × 2/5

Model shows 3 groups of 2/5

Count: 2 + 2 + 2 = 6 shaded parts

Denominator stays 5

Answer: 6/5 = 1 1/5

3. Multiply Fractions by Whole Numbers Using Number Lines

Definition: Use a number line to show repeated addition of fractions through equal jumps.

📝 Steps Using Number Lines:

  1. Draw a number line starting at 0
  2. Mark equal intervals based on the denominator
  3. Make jumps equal to the fraction size
  4. Count how many jumps (equal to whole number)
  5. Where you land is the answer

✏️ Example: 4 × 1/3

Start at 0 on number line

Make 4 jumps of 1/3 each:

Jump 1: 0 → 1/3

Jump 2: 1/3 → 2/3

Jump 3: 2/3 → 3/3 (which is 1)

Jump 4: 1 → 1 1/3

Answer: 4/3 = 1 1/3

4. Multiples of Fractions: Find the Missing Numbers

Definition: Multiples of a fraction are found by multiplying the fraction by different whole numbers.

🔑 Pattern of Multiples:

For fraction 2/3:

1 × 2/3 = 2/3

2 × 2/3 = 4/3 = 1 1/3

3 × 2/3 = 6/3 = 2

4 × 2/3 = 8/3 = 2 2/3

5 × 2/3 = 10/3 = 3 1/3

💡 Finding Missing Numbers:

If ___ × 3/4 = 9/4, find the missing number:

Divide: 9 ÷ 3 = 3

Answer: 3

5. Multiply Fractions by Whole Numbers Using Arrays

Definition: Arrays organize objects in rows and columns to show multiplication of fractions by whole numbers.

📝 Array Model Steps:

  1. Create rows equal to the whole number
  2. Divide each row by the denominator
  3. Shade parts according to the numerator in each row
  4. Count total shaded parts
  5. Write as a fraction with same denominator

✏️ Example: 3 × 2/5 using array

Draw 3 rows (for 3 groups)

Divide each row into 5 parts

Shade 2 parts in each row

Total shaded: 2 + 2 + 2 = 6 parts

Answer: 6/5 = 1 1/5

6. Fractions of a Number: Model and Multiply

Definition: Finding a fraction of a whole number means dividing the whole into equal parts and taking some of those parts.

📐 Formula:

Fraction × Whole Number = (Numerator × Whole Number) / Denominator

✏️ Example: Find 2/3 of 12

Method 1 (Division first):

Divide 12 into 3 equal parts: 12 ÷ 3 = 4

Take 2 of those parts: 4 × 2 = 8

Method 2 (Formula):

2/3 × 12 = (2 × 12) / 3 = 24 / 3 = 8

Answer: 8

7. Multiply Two Unit Fractions Using Models

Definition: A unit fraction has a numerator of 1. When multiplying two unit fractions, we use area models to find the overlapping region.

📝 Area Model Steps:

  1. Draw a rectangle (unit whole)
  2. Divide vertically for first denominator
  3. Shade columns for first numerator (1 column)
  4. Divide horizontally for second denominator
  5. Shade rows for second numerator (1 row)
  6. Count the overlapping shaded region

Formula: 1/a × 1/b = 1/(a × b)

✏️ Example: 1/3 × 1/4

Draw rectangle divided into 3 columns (1/3)

Shade 1 column

Divide into 4 rows (1/4)

Shade 1 row

Overlap = 1 piece out of 12 total pieces

Answer: 1/12

8. Multiply Two Fractions Using Models

Definition: When multiplying any two fractions, use the area model to find where the shaded regions overlap.

📐 General Formula:

a/b × c/d = (a × c)/(b × d)

Multiply numerators, multiply denominators

✏️ Example: 2/3 × 3/4 using area model

Step 1: Draw rectangle, divide into 3 columns

Step 2: Shade 2 of 3 columns (for 2/3)

Step 3: Divide into 4 rows

Step 4: Shade 3 of 4 rows (for 3/4)

Step 5: Count overlapping squares: 6 shaded

Step 6: Total squares: 3 × 4 = 12

Using formula: (2 × 3)/(3 × 4) = 6/12 = 1/2

Answer: 6/12 = 1/2

9. Multiply Fractions Greater Than One Using Models

Definition: When fractions are greater than 1 (improper fractions or mixed numbers), we need multiple whole rectangles to model the multiplication.

📝 Steps for Fractions > 1:

  1. Convert mixed numbers to improper fractions (if needed)
  2. Draw multiple rectangles for wholes
  3. Apply area model technique
  4. Count all overlapping shaded regions
  5. Convert back to mixed number if needed

✏️ Example: 1 1/2 × 2/3

Step 1: Convert 1 1/2 to improper fraction: 3/2

Step 2: Draw 2 rectangles (for 3/2, which is more than 1)

Step 3: Divide each into 2 columns, shade 3 columns total

Step 4: Divide into 3 rows, shade 2 rows

Step 5: Count overlap: 6 pieces out of 12

Using formula: 3/2 × 2/3 = (3 × 2)/(2 × 3) = 6/6 = 1

Answer: 1

Key Formulas for Fraction Multiplication

TypeFormulaExample
Fraction × Wholea/b × n = (a × n)/b2/3 × 4 = 8/3
Fraction × Fractiona/b × c/d = (a×c)/(b×d)2/3 × 3/4 = 6/12
Unit Fractions1/a × 1/b = 1/(a×b)1/2 × 1/5 = 1/10

Quick Reference Chart

Model TypeBest Used ForWhat It Shows
Number LineFraction × WholeRepeated addition/jumps
Array ModelFraction × WholeGroups in rows/columns
Area ModelFraction × FractionOverlapping regions
Circle/Bar ModelFinding part of wholeVisual fractions

💡 Key Concepts to Remember:

Multiplication = Repeated Addition

4 × 2/3 = 2/3 + 2/3 + 2/3 + 2/3

Multiply Across

Numerator × Numerator / Denominator × Denominator

Simplify

Always reduce to lowest terms

Area Model

Overlap = Product

🔑 Key Tips for Success:

  • When multiplying by a whole number, multiply only the numerator
  • For fraction × fraction, multiply numerators together and denominators together
  • Use visual models to understand what multiplication means
  • The word "of" in word problems often means multiply (1/2 of 12 = 1/2 × 12)
  • Always simplify your final answer to lowest terms
  • Convert improper fractions to mixed numbers when appropriate
  • Practice with different models to build deep understanding

📚 Fifth Grade Understand Fraction Multiplication - Complete Study Guide

Master these concepts for math excellence! ✨

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