Divide Decimals - Fifth Grade Math
Complete Notes & Formulas
1. Estimate Decimal Quotients
What is Estimation?
Estimation means finding an approximate answer by rounding decimals before dividing.
Two Methods for Estimation
Method 1: Rounding
Step 1: Round the dividend (number being divided) to the nearest whole number
Step 2: Round the divisor (number dividing by) to the nearest whole number
Step 3: Divide the rounded numbers
Method 2: Compatible Numbers
Compatible numbers are numbers that are easy to divide mentally. They divide evenly with no remainder.
Step 1: Find compatible numbers close to the actual numbers
Step 2: Use basic division facts
Step 3: Calculate the quotient
Formula
Examples
Example 1 (Rounding): Estimate 62.9 ÷ 7.48
• 62.9 rounds to 63
• 7.48 rounds to 7
• 63 ÷ 7 = 9
Estimated Quotient ≈ 9
Example 2 (Compatible Numbers): Estimate 23.8 ÷ 4.75
• 23.8 is close to 24
• 4.75 is close to 4
• 24 and 4 are compatible (24 ÷ 4 = 6)
Estimated Quotient ≈ 6
When to Use Estimation
✓ To check if your answer is reasonable
✓ When an approximate answer is acceptable
✗ Do NOT use when exact answers are required
2. Divide Decimals Using Blocks: Complete the Equation
Base Ten Blocks Representation
Flat = 1 whole = 1.0
Rod (Long) = 1 tenth = 0.1
Cube (Unit) = 1 hundredth = 0.01
Steps to Divide Using Blocks
Step 1: Represent the dividend (number being divided) using base ten blocks
Step 2: Divide the blocks into equal groups based on the divisor
Step 3: If needed, trade larger blocks for smaller ones (1 flat = 10 rods, 1 rod = 10 cubes)
Step 4: Distribute all blocks equally into groups
Step 5: Count the value in ONE group to find the quotient
Key Concept
Examples
Example 1: 1.4 ÷ 7 = ?
• Represent 1.4 → 1 flat + 4 rods
• Trade 1 flat for 10 rods → Total: 14 rods (14 tenths)
• Divide 14 rods into 7 equal groups
• Each group has 2 rods = 0.2
Answer: 1.4 ÷ 7 = 0.2
Example 2: 0.63 ÷ 3 = ?
• Represent 0.63 → 6 rods + 3 cubes
• Divide 6 rods into 3 groups → 2 rods per group
• Divide 3 cubes into 3 groups → 1 cube per group
• Each group has 2 rods + 1 cube = 0.2 + 0.01 = 0.21
Answer: 0.63 ÷ 3 = 0.21
3. Divide Decimals Using Area Models: Complete the Equation
What is an Area Model?
An area model represents division as a rectangle where the area is the dividend, one side is the divisor, and the other side is the quotient.
Area = Length × Width
Dividend = Divisor × Quotient
Steps to Use Area Model
Step 1: Treat decimals as whole numbers temporarily
Step 2: Break the dividend into parts that are easier to divide
Step 3: Divide each part by the divisor
Step 4: Add the partial quotients together
Step 5: Place the decimal point in the correct position
Example
Divide: 225.5 ÷ 5
Step 1: Remove decimal: 2255 ÷ 5
Step 2: Break 2255 into parts: 2000 + 200 + 50 + 5
Step 3: Divide each part:
2000 ÷ 5 = 400
200 ÷ 5 = 40
50 ÷ 5 = 10
5 ÷ 5 = 1
Step 4: Add: 400 + 40 + 10 + 1 = 451
Step 5: Place decimal: 225.5 ÷ 5 = 45.1
Answer: 45.1
4. Divide Decimals by Whole Numbers Using Place Value
The Place Value Method
This method uses understanding of place value to divide decimals mentally or with simple calculations.
Key Rules
• Think about the dividend in terms of its place value units (ones, tenths, hundredths)
• Convert to the same unit (all tenths, all hundredths, etc.)
• Divide as whole numbers, then adjust the place value
Steps
Step 1: Identify the place value of the decimal
Step 2: Think of the decimal as a whole number (in tenths, hundredths, etc.)
Step 3: Divide the whole numbers
Step 4: Adjust the answer to match the place value
Examples
Example 1: 8.4 ÷ 2
• 8.4 = 84 tenths
• 84 tenths ÷ 2 = 42 tenths
• 42 tenths = 4.2
Answer: 4.2
Example 2: 0.48 ÷ 4
• 0.48 = 48 hundredths
• 48 hundredths ÷ 4 = 12 hundredths
• 12 hundredths = 0.12
Answer: 0.12
5. Divide Decimals by Whole Numbers Without Adding Zeros
What Does This Mean?
These are division problems where the decimal divides evenly without a remainder, so no extra zeros are needed.
Long Division Steps
Step 1: Set up the division problem (dividend inside, divisor outside)
Step 2: Place the decimal point in the quotient directly above the decimal in the dividend
Step 3: Divide as if working with whole numbers
Step 4: Bring down digits one at a time
Step 5: Continue until remainder is 0
Key Rule
Examples
Example 1: 8.4 ÷ 4
• 4 ) 8.4
• 8 ÷ 4 = 2 (place above the 8)
• Place decimal point above dividend's decimal
• Bring down 4: 4 ÷ 4 = 1
• Answer: 2.1
Example 2: 6.75 ÷ 5
• 6 ÷ 5 = 1 remainder 1
• Bring down 7: 17 ÷ 5 = 3 remainder 2
• Place decimal point
• Bring down 5: 25 ÷ 5 = 5
• Answer: 1.35
6. Division with Decimal Quotients
What is a Decimal Quotient?
A decimal quotient is an answer that includes a decimal point, even when dividing two whole numbers.
When Do We Get Decimal Quotients?
• When the dividend doesn't divide evenly by the divisor
• When we continue dividing past the whole number part
• When we add zeros to the dividend to continue dividing
Steps
Step 1: Divide as usual with whole numbers
Step 2: If there's a remainder, add a decimal point to the quotient
Step 3: Add a zero to the dividend after the decimal point
Step 4: Bring down the zero and continue dividing
Step 5: Repeat until remainder is 0 or you have enough decimal places
Formula
Examples
Example 1: 7 ÷ 4
• 7 ÷ 4 = 1 remainder 3
• Add decimal: 1.
• Add zero to dividend: 7.0 → bring down 0 → 30
• 30 ÷ 4 = 7 remainder 2
• Add another zero: 20 ÷ 4 = 5
• Answer: 1.75
Example 2: 9 ÷ 8
• 9 ÷ 8 = 1 remainder 1
• Add decimal and zero: 1._ → 10 ÷ 8 = 1 remainder 2
• Add another zero: 20 ÷ 8 = 2 remainder 4
• Add another zero: 40 ÷ 8 = 5
• Answer: 1.125
7. Division with Decimal Quotients and Rounding
Why Round?
Sometimes division produces a quotient with too many decimal places or a quotient that repeats forever. We round to make it more practical.
Rounding Rules
If the digit to the right is 5 or greater → Round UP (add 1 to the rounding place)
If the digit to the right is less than 5 → Round DOWN (keep the digit the same)
Common Rounding Places
• Nearest tenth: 1 decimal place (0.1)
• Nearest hundredth: 2 decimal places (0.01)
• Nearest thousandth: 3 decimal places (0.001)
Steps
Step 1: Divide until you have one more decimal place than needed
Step 2: Look at the digit in the place right after your rounding place
Step 3: Apply the rounding rule
Step 4: Drop all digits after the rounding place
Examples
Example 1: 10 ÷ 3 (round to nearest hundredth)
• 10 ÷ 3 = 3.333333... (repeating)
• Divide to 3 decimal places: 3.333
• Look at third decimal place: 3
• 3 < 5, so round DOWN
• Answer: 3.33
Example 2: 22 ÷ 7 (round to nearest tenth)
• 22 ÷ 7 = 3.142857...
• Divide to 2 decimal places: 3.14
• Look at hundredths place: 4
• 4 < 5, so round DOWN
• Answer: 3.1
8. Division with Decimal Quotients: Word Problems
Key Words for Division
• Shared equally
• Divided into groups
• Each person gets
• Per, each, every
• How many in each?
• Average, mean
Steps to Solve Word Problems
Step 1: Read the problem carefully
Step 2: Identify what you're trying to find
Step 3: Find the dividend (total amount) and divisor (number of groups)
Step 4: Write the division equation
Step 5: Solve and check if the answer makes sense
Examples
Example 1: Sarah bought 5 pounds of apples for $8.75. What is the cost per pound?
• Find: Cost per pound
• Total cost: $8.75 (dividend)
• Number of pounds: 5 (divisor)
• Equation: $8.75 ÷ 5
• Calculate: 8.75 ÷ 5 = 1.75
• Answer: $1.75 per pound
Example 2: A ribbon is 12.6 meters long. It is cut into 9 equal pieces. How long is each piece?
• Find: Length of each piece
• Total length: 12.6 meters (dividend)
• Number of pieces: 9 (divisor)
• Equation: 12.6 ÷ 9
• Calculate: 12.6 ÷ 9 = 1.4
• Answer: 1.4 meters per piece
9. Divide by Decimals Using Place Value
The Key Concept
To divide by a decimal, convert the divisor to a whole number by multiplying BOTH the dividend and divisor by the same power of 10.
Why Does This Work?
Multiplying both numbers by the same amount doesn't change the quotient. It's like equivalent fractions!
6 ÷ 2 = 3
(6 × 10) ÷ (2 × 10) = 60 ÷ 20 = 3
Same answer!
Steps
Step 1: Count how many decimal places are in the divisor
Step 2: Move the decimal point in the divisor to the RIGHT to make it a whole number
Step 3: Move the decimal point in the dividend to the RIGHT the same number of places
Step 4: Divide as usual with the new numbers
Examples
Example 1: 4.5 ÷ 0.5
• Divisor 0.5 has 1 decimal place
• Move decimal 1 place RIGHT in both numbers:
→ 0.5 becomes 5
→ 4.5 becomes 45
• Now divide: 45 ÷ 5 = 9
• Answer: 9
Example 2: 0.63 ÷ 0.09
• Divisor 0.09 has 2 decimal places
• Move decimal 2 places RIGHT in both:
→ 0.09 becomes 9
→ 0.63 becomes 63
• Now divide: 63 ÷ 9 = 7
• Answer: 7
10. Divide by Decimals Without Adding Zeros
What This Means
These problems divide evenly after converting the divisor to a whole number, so no extra zeros are needed in the dividend.
Steps
Step 1: Move the decimal in the divisor to make it a whole number
Step 2: Move the decimal in the dividend the same number of places
Step 3: Place the decimal point in the quotient above the new position in the dividend
Step 4: Divide as usual
Step 5: The division completes with no remainder
Examples
Example 1: 3.6 ÷ 1.2
• Move decimal 1 place RIGHT:
→ 1.2 becomes 12
→ 3.6 becomes 36
• Divide: 36 ÷ 12 = 3
• Answer: 3
Example 2: 8.4 ÷ 0.7
• Move decimal 1 place RIGHT:
→ 0.7 becomes 7
→ 8.4 becomes 84
• Divide: 84 ÷ 7 = 12
• Answer: 12
11. Divide by Decimals (Complete Method)
The Universal Rule
Make the divisor a whole number, then divide!
Complete Steps
Step 1: Write the division problem
Step 2: Count decimal places in the divisor
Step 3: Move both decimal points RIGHT by that amount
Step 4: Add zeros to the dividend if needed
Step 5: Place the decimal point in the quotient
Step 6: Divide using long division
Step 7: Add zeros after the dividend's decimal point if there's a remainder
Step 8: Continue until remainder is 0 or round as instructed
Examples
Example 1: 5.75 ÷ 2.5
• Divisor has 1 decimal place
• Move decimals 1 place RIGHT:
→ 2.5 becomes 25
→ 5.75 becomes 57.5
• Divide: 57.5 ÷ 25
• 575 ÷ 25 = 23 (thinking in tenths)
• Place decimal: 2.3
• Answer: 2.3
Example 2: 7.65 ÷ 0.15
• Divisor has 2 decimal places
• Move decimals 2 places RIGHT:
→ 0.15 becomes 15
→ 7.65 becomes 765
• Divide: 765 ÷ 15 = 51
• Answer: 51
Quick Reference: Division Steps Summary
Division Type | Key Step | Example |
---|---|---|
Decimal ÷ Whole Number | Keep decimal point aligned | 6.4 ÷ 2 = 3.2 |
Whole Number ÷ Whole Number | Add zeros after decimal if needed | 7 ÷ 4 = 1.75 |
Decimal ÷ Decimal | Make divisor a whole number first | 4.8 ÷ 0.6 = 8 |
💡 Important Tips to Remember
✓ Always make the divisor a whole number when dividing by decimals
✓ Move decimal points the same number of places in both dividend and divisor
✓ Line up the decimal point in your quotient with the decimal in the dividend
✓ Add zeros to the dividend if needed to continue dividing
✓ Use estimation to check if your answer is reasonable
✓ When rounding, divide to one more place than required
✓ In word problems, identify key words that signal division
✓ Check your work by multiplying: quotient × divisor should equal dividend
🧠 Memory Tricks for Decimal Division
Trick 1: "Move Move Divide"
When dividing by a decimal: Move the decimal in the divisor, move it the same way in the dividend, then divide!
Trick 2: "Straight Up"
The decimal point in your answer goes straight up from the decimal point in the dividend.
Trick 3: "Make It Whole"
Always turn the divisor into a whole number first—it makes division much easier!
Trick 4: "Check with Multiplication"
Answer × Divisor = Dividend (If it doesn't, check your work!)
Master Decimal Division! 🎯
Practice different types of problems daily to build confidence and speed!