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:
- Look at the model shown
- Count how many groups are shaded
- Count total shaded parts (numerator)
- Identify the denominator (parts in each whole)
- 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:
- Draw a number line starting at 0
- Mark equal intervals based on the denominator
- Make jumps equal to the fraction size
- Count how many jumps (equal to whole number)
- 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:
- Create rows equal to the whole number
- Divide each row by the denominator
- Shade parts according to the numerator in each row
- Count total shaded parts
- 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:
- Draw a rectangle (unit whole)
- Divide vertically for first denominator
- Shade columns for first numerator (1 column)
- Divide horizontally for second denominator
- Shade rows for second numerator (1 row)
- 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:
- Convert mixed numbers to improper fractions (if needed)
- Draw multiple rectangles for wholes
- Apply area model technique
- Count all overlapping shaded regions
- 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
Type | Formula | Example |
---|---|---|
Fraction × Whole | a/b × n = (a × n)/b | 2/3 × 4 = 8/3 |
Fraction × Fraction | a/b × c/d = (a×c)/(b×d) | 2/3 × 3/4 = 6/12 |
Unit Fractions | 1/a × 1/b = 1/(a×b) | 1/2 × 1/5 = 1/10 |
Quick Reference Chart
Model Type | Best Used For | What It Shows |
---|---|---|
Number Line | Fraction × Whole | Repeated addition/jumps |
Array Model | Fraction × Whole | Groups in rows/columns |
Area Model | Fraction × Fraction | Overlapping regions |
Circle/Bar Model | Finding part of whole | Visual 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! ✨