📊 Convert Between Decimals and Fractions
Complete Notes & Formulae for Fifth Grade Math Students
1️⃣ Model Decimals and Fractions
Understanding the Connection
Decimals and fractions are two different ways to represent the same parts of a whole. We can visualize them using models like grids, number lines, and area models.
Place Value Chart
Ones | Decimal Point | Tenths | Hundredths | Thousandths |
---|---|---|---|---|
1 | . | $\frac{1}{10}$ | $\frac{1}{100}$ | $\frac{1}{1000}$ |
— | . | 0.1 | 0.01 | 0.001 |
Visual Models:
- Area Model: A square or rectangle divided into equal parts (shaded parts show the fraction/decimal)
- Number Line: Points between 0 and 1 represent fractions and decimals
- Base-10 Blocks: Flats, rods, and units represent ones, tenths, and hundredths
Example:
A grid with 100 squares where 25 are shaded shows:
$\frac{25}{100}$ = 0.25 = twenty-five hundredths
2️⃣ Convert Fractions to Decimals
What Does It Mean?
Converting a fraction to a decimal means rewriting the fraction as a decimal number. There are two main methods to do this.
$\frac{\text{numerator}}{\text{denominator}}$ = numerator ÷ denominator
Method 1: Using Place Value (Base-10 Fractions)
When to use: When the denominator is 10, 100, or 1000
1Look at the denominator
- If denominator = 10 → tenths place → 1 decimal digit
- If denominator = 100 → hundredths place → 2 decimal digits
- If denominator = 1000 → thousandths place → 3 decimal digits
2Write the numerator with the decimal point in the correct place
Examples:
$\frac{7}{10}$ = 0.7 (seven tenths)
$\frac{37}{100}$ = 0.37 (thirty-seven hundredths)
$\frac{5}{1000}$ = 0.005 (five thousandths)
$\frac{603}{1000}$ = 0.603 (six hundred three thousandths)
Method 2: Division Method (Any Fraction)
When to use: When the denominator is NOT 10, 100, or 1000
1Divide the numerator by the denominator
Example 1: Convert $\frac{3}{4}$ to a decimal
$3 ÷ 4 = 0.75$
Example 2: Convert $\frac{1}{2}$ to a decimal
$1 ÷ 2 = 0.5$
Example 3: Convert $\frac{5}{8}$ to a decimal
$5 ÷ 8 = 0.625$
Method 3: Finding Equivalent Fractions
When to use: When you can easily convert the denominator to 10, 100, or 1000
1Find what to multiply the denominator by to get 10, 100, or 1000
2Multiply both numerator and denominator by that number
3Write as a decimal using Method 1
Example 1: Convert $\frac{1}{5}$ to a decimal
$\frac{1}{5} = \frac{1 \times 2}{5 \times 2} = \frac{2}{10} = 0.2$
Example 2: Convert $\frac{3}{20}$ to a decimal
$\frac{3}{20} = \frac{3 \times 5}{20 \times 5} = \frac{15}{100} = 0.15$
3️⃣ Convert Mixed Numbers to Decimals
What is a Mixed Number?
A mixed number has a whole number part and a fraction part. For example: $2\frac{3}{4}$ (two and three-fourths).
Whole Number + (Fraction → Decimal) = Mixed Number as Decimal
Step-by-Step Process:
1Write down the whole number
2Convert the fraction part to a decimal (use methods from Topic 2)
3Add the whole number and the decimal together
Example 1: Convert $1\frac{88}{100}$ to a decimal
Step 1: Whole number = 1
Step 2: $\frac{88}{100} = 0.88$
Step 3: $1 + 0.88 = 1.88$
Example 2: Convert $3\frac{1}{4}$ to a decimal
Step 1: Whole number = 3
Step 2: $\frac{1}{4} = 1 ÷ 4 = 0.25$
Step 3: $3 + 0.25 = 3.25$
Example 3: Convert $9\frac{5}{10}$ to a decimal
Step 1: Whole number = 9
Step 2: $\frac{5}{10} = 0.5$
Step 3: $9 + 0.5 = 9.5$
Example 4: Convert $5\frac{3}{8}$ to a decimal
Step 1: Whole number = 5
Step 2: $\frac{3}{8} = 3 ÷ 8 = 0.375$
Step 3: $5 + 0.375 = 5.375$
4️⃣ Convert Decimals to Fractions
The Key Strategy:
Read the decimal out loud! The way you say it tells you what fraction to write.
1. Read the decimal → 2. Write as fraction → 3. Simplify (if possible)
Step 1: Read the Decimal and Identify Place Value
Number of Decimal Places | Place Value Name | Denominator |
---|---|---|
1 digit after decimal | tenths | 10 |
2 digits after decimal | hundredths | 100 |
3 digits after decimal | thousandths | 1000 |
Step 2: Write the Fraction
The numbers after the decimal = Numerator (top)
The place value = Denominator (bottom)
Example 1: Convert 0.7 to a fraction
Read: "seven tenths"
Write: $\frac{7}{10}$
✅ Already simplified!
Example 2: Convert 0.45 to a fraction
Read: "forty-five hundredths"
Write: $\frac{45}{100}$
Simplify: $\frac{45 ÷ 5}{100 ÷ 5} = \frac{9}{20}$
Example 3: Convert 0.125 to a fraction
Read: "one hundred twenty-five thousandths"
Write: $\frac{125}{1000}$
Simplify: $\frac{125 ÷ 125}{1000 ÷ 125} = \frac{1}{8}$
Example 4: Convert 0.04 to a fraction
Read: "four hundredths"
Write: $\frac{4}{100}$
Simplify: $\frac{4 ÷ 4}{100 ÷ 4} = \frac{1}{25}$
Step 3: Simplify the Fraction
To simplify a fraction:
- Find the Greatest Common Factor (GCF) of the numerator and denominator
- Divide both the numerator and denominator by the GCF
Example: Simplify $\frac{50}{100}$
GCF of 50 and 100 = 50
$\frac{50 ÷ 50}{100 ÷ 50} = \frac{1}{2}$
5️⃣ Convert Decimals to Mixed Numbers
What is Special About These Decimals?
When a decimal is greater than 1 (like 2.75 or 4.3), we can write it as a mixed number instead of an improper fraction.
Decimal → Whole Number $\frac{\text{fraction}}{\text{ }}$
Step-by-Step Process:
1The whole number part stays the same
Everything before the decimal point = whole number
2Convert the decimal part to a fraction
Use the same method as Topic 4
3Simplify the fraction (if possible)
Example 1: Convert 1.37 to a mixed number
Step 1: Whole number = 1
Step 2: 0.37 = "thirty-seven hundredths" = $\frac{37}{100}$
Step 3: Cannot simplify
Answer: $1\frac{37}{100}$
Example 2: Convert 3.5 to a mixed number
Step 1: Whole number = 3
Step 2: 0.5 = "five tenths" = $\frac{5}{10}$
Step 3: Simplify: $\frac{5}{10} = \frac{1}{2}$
Answer: $3\frac{1}{2}$
Example 3: Convert 2.75 to a mixed number
Step 1: Whole number = 2
Step 2: 0.75 = "seventy-five hundredths" = $\frac{75}{100}$
Step 3: Simplify: $\frac{75}{100} = \frac{3}{4}$ (divide by 25)
Answer: $2\frac{3}{4}$
Example 4: Convert 5.008 to a mixed number
Step 1: Whole number = 5
Step 2: 0.008 = "eight thousandths" = $\frac{8}{1000}$
Step 3: Simplify: $\frac{8}{1000} = \frac{1}{125}$ (divide by 8)
Answer: $5\frac{1}{125}$
📋 Quick Reference Table
Decimal | Fraction | Mixed Number (if applicable) | Read As |
---|---|---|---|
0.1 | $\frac{1}{10}$ | — | one tenth |
0.5 | $\frac{5}{10} = \frac{1}{2}$ | — | five tenths / one half |
0.25 | $\frac{25}{100} = \frac{1}{4}$ | — | twenty-five hundredths |
0.75 | $\frac{75}{100} = \frac{3}{4}$ | — | seventy-five hundredths |
1.5 | $\frac{15}{10} = \frac{3}{2}$ | $1\frac{1}{2}$ | one and five tenths |
2.25 | $\frac{225}{100} = \frac{9}{4}$ | $2\frac{1}{4}$ | two and twenty-five hundredths |
⭐ Common Equivalent Values to Memorize
Fraction | Decimal | Visual |
---|---|---|
$\frac{1}{2}$ | 0.5 | half |
$\frac{1}{4}$ | 0.25 | one quarter |
$\frac{3}{4}$ | 0.75 | three quarters |
$\frac{1}{5}$ | 0.2 | one fifth |
$\frac{1}{10}$ | 0.1 | one tenth |
$\frac{1}{100}$ | 0.01 | one hundredth |
💡 Important Tips & Tricks
🎯 Ready to Practice?
Try these conversions on your own:
1. Convert $\frac{3}{5}$ to a decimal
2. Convert 0.8 to a fraction
3. Convert $4\frac{2}{5}$ to a decimal
4. Convert 3.65 to a mixed number
5. Convert 0.125 to a simplified fraction
Answers: 1) 0.6 | 2) $\frac{4}{5}$ | 3) 4.4 | 4) $3\frac{13}{20}$ | 5) $\frac{1}{8}$