Convert between decimals and fractions | 5th Grade Math

📊 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.

Key Concept: Both decimals and fractions show parts of a whole number. The decimal point separates whole numbers from parts, while fractions show parts using a numerator (top) and denominator (bottom).

Place Value Chart

OnesDecimal PointTenthsHundredthsThousandths
1.$\frac{1}{10}$$\frac{1}{100}$$\frac{1}{1000}$
.0.10.010.001

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.

Main Formula:
$\frac{\text{numerator}}{\text{denominator}}$ = 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

$\frac{3}{20} = \frac{3 \times 5}{20 \times 5} = \frac{15}{100} = 0.15$

Remember: The fraction bar means "divided by," so $\frac{3}{4}$ is the same as $3 ÷ 4$

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).

Steps to Convert:

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: $5 + 0.375 = 5.375$

Quick Tip: The whole number becomes the digit(s) before the decimal point, and the fraction becomes the digits after the decimal point!

4️⃣ Convert Decimals to Fractions

The Key Strategy:

Read the decimal out loud! The way you say it tells you what fraction to write.

3-Step Process:

1. Read the decimal → 2. Write as fraction → 3. Simplify (if possible)

Step 1: Read the Decimal and Identify Place Value

Number of Decimal PlacesPlace Value NameDenominator
1 digit after decimaltenths10
2 digits after decimalhundredths100
3 digits after decimalthousandths1000

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:

  1. Find the Greatest Common Factor (GCF) of the numerator and denominator
  2. Divide both the numerator and denominator by the GCF

Example: Simplify $\frac{50}{100}$

GCF of 50 and 100 = 50
$\frac{50 ÷ 50}{100 ÷ 50} = \frac{1}{2}$

Pro Tip: Count the digits after the decimal point. That tells you how many zeros are in your denominator!

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.

Format:

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: $5\frac{1}{125}$

Remember: A mixed number is just another way to write a decimal greater than 1. Both forms represent the same value!

📋 Quick Reference Table

DecimalFractionMixed 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

FractionDecimalVisual
$\frac{1}{2}$0.5half
$\frac{1}{4}$0.25one quarter
$\frac{3}{4}$0.75three quarters
$\frac{1}{5}$0.2one fifth
$\frac{1}{10}$0.1one tenth
$\frac{1}{100}$0.01one hundredth

💡 Important Tips & Tricks

Tip 1: Always simplify fractions to their lowest terms. Divide the numerator and denominator by their Greatest Common Factor (GCF).
Tip 2: When converting fractions to decimals, if division doesn't end, you may get a repeating decimal (like $\frac{1}{3} = 0.333...$).
Tip 3: To check your work, convert back! If you changed a fraction to a decimal, convert that decimal back to a fraction to see if you get the original.
Tip 4: The word "and" in a decimal reading tells you where the decimal point is. For example, "two and three tenths" = $2.3$
Tip 5: Count decimal places to find the denominator: 1 place = 10, 2 places = 100, 3 places = 1000

🎯 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) $\frac{1}{8}$