Mixed Operations: Decimals - Fifth Grade Math
Complete Notes & Formulas
1. Add, Subtract, Multiply, and Divide Decimals (Mixed Operations)
The Order of Operations: PEMDAS / BODMAS
When solving problems with multiple operations, you must follow the correct order to get the right answer.
PEMDAS Order
P - Parentheses ( )
E - Exponents (Powers)
M & D - Multiplication and Division (Left to Right)
A & S - Addition and Subtraction (Left to Right)
BODMAS Order (Alternative)
B - Brackets [ ]
O - Orders (Powers/Exponents)
D & M - Division and Multiplication (Left to Right)
A & S - Addition and Subtraction (Left to Right)
Important Rules
• Always solve parentheses FIRST
• Multiplication and Division have equal priority - work from LEFT to RIGHT
• Addition and Subtraction have equal priority - work from LEFT to RIGHT
• The order stays the same for decimals as it does for whole numbers
Step-by-Step Process
Step 1: Look for PARENTHESES ( ) and solve what's inside first
Step 2: Solve any EXPONENTS (powers)
Step 3: Do all MULTIPLICATION and DIVISION from left to right
Step 4: Do all ADDITION and SUBTRACTION from left to right
Step 5: Write your final answer
Examples
Example 1: 5.2 + 3.6 × 2.5
Step 1: No parentheses
Step 2: No exponents
Step 3: Multiply first: 3.6 × 2.5 = 9.0
Step 4: Now add: 5.2 + 9.0 = 14.2
Answer: 14.2
Example 2: (8.5 - 3.2) × 2.0 + 4.6
Step 1: Solve parentheses: 8.5 - 3.2 = 5.3
Expression becomes: 5.3 × 2.0 + 4.6
Step 2: Multiply: 5.3 × 2.0 = 10.6
Expression becomes: 10.6 + 4.6
Step 3: Add: 10.6 + 4.6 = 15.2
Answer: 15.2
Example 3: 18.0 ÷ 3.6 - 1.5 × 0.4
Step 1: No parentheses
Step 2: Division first (left to right): 18.0 ÷ 3.6 = 5.0
Step 3: Multiplication next: 1.5 × 0.4 = 0.6
Expression becomes: 5.0 - 0.6
Step 4: Subtract: 5.0 - 0.6 = 4.4
Answer: 4.4
Example 4: 12.5 - 4.2 ÷ 6.0 + 1.3 × 0.4
Step 1: Division: 4.2 ÷ 6.0 = 0.7
Step 2: Multiplication: 1.3 × 0.4 = 0.52
Expression becomes: 12.5 - 0.7 + 0.52
Step 3: Subtract (left to right): 12.5 - 0.7 = 11.8
Step 4: Add: 11.8 + 0.52 = 12.32
Answer: 12.32
Common Mistakes to Avoid
✗ DON'T work from left to right for all operations
✗ DON'T forget parentheses come first
✗ DON'T do addition before multiplication
✓ DO follow PEMDAS/BODMAS order strictly
2. Add, Subtract, Multiply, and Divide Decimals: Word Problems
Identifying Operations in Word Problems
Operation | Key Words/Phrases |
---|---|
Addition (+) | Total, sum, altogether, combined, in all, plus, more than, increase |
Subtraction (−) | Difference, less than, minus, decrease, take away, left, remaining, how many more |
Multiplication (×) | Times, product, of, each, per, groups of, repeated addition |
Division (÷) | Divided by, shared equally, quotient, per, each, average, split |
Steps to Solve Word Problems
Step 1: Read the problem carefully (maybe twice!)
Step 2: Identify what you need to find (the question)
Step 3: Find the important numbers and information
Step 4: Determine which operation(s) to use
Step 5: Set up the equation
Step 6: Solve using the correct order of operations
Step 7: Check if your answer makes sense
Step 8: Write your answer with the correct unit
Examples
Example 1 (Addition & Multiplication):
"Sarah bought 3 notebooks for $2.45 each and a pen for $1.75. How much did she spend in total?"
Step 1: Find total cost
Step 2: Cost of notebooks: 3 × $2.45
Step 3: Add pen cost: + $1.75
Equation: (3 × 2.45) + 1.75
Solve: 7.35 + 1.75 = 9.10
Answer: $9.10
Example 2 (Subtraction & Division):
"A 6.5-meter rope is cut into 5 equal pieces. If 0.8 meters is wasted, how long is each piece?"
Step 1: Find usable rope: 6.5 - 0.8 = 5.7 meters
Step 2: Divide by 5 pieces: 5.7 ÷ 5
Equation: (6.5 - 0.8) ÷ 5
Solve: 5.7 ÷ 5 = 1.14
Answer: 1.14 meters per piece
Example 3 (Mixed Operations):
"A store sells juice boxes for $0.75 each. Tom bought 8 boxes and paid with a $10 bill. How much change did he receive?"
Step 1: Cost of juice boxes: 8 × 0.75 = 6.00
Step 2: Change: 10.00 - 6.00
Equation: 10.00 - (8 × 0.75)
Solve: 10.00 - 6.00 = 4.00
Answer: $4.00 change
3. Add, Subtract, Multiply, and Divide Decimals: Multi-Step Word Problems
What are Multi-Step Problems?
Multi-step word problems require you to perform more than one operation to find the answer. You must solve the problem in steps, one at a time.
Strategy for Multi-Step Problems
1. Break it down: Identify each step needed to solve
2. Order matters: Determine which calculation to do first, second, third, etc.
3. Write intermediate steps: Write down each step's answer before moving to the next
4. Use parentheses: Group operations that should be done together
5. Check your work: Make sure the final answer makes sense
Step-by-Step Approach
Step 1: Read the entire problem carefully
Step 2: Underline or highlight important information
Step 3: Identify what the question is asking
Step 4: List all the steps needed in order
Step 5: Solve one step at a time
Step 6: Use each answer in the next step
Step 7: Write the final answer with units
Examples
Example 1:
"Maria went to the grocery store with $50.00. She bought 4 apples for $1.25 each, 2 loaves of bread for $3.50 each, and a gallon of milk for $4.75. How much money does she have left?"
Step 1: Find the cost of apples
4 × $1.25 = $5.00
Step 2: Find the cost of bread
2 × $3.50 = $7.00
Step 3: Find total spent
$5.00 + $7.00 + $4.75 = $16.75
Step 4: Find money left
$50.00 - $16.75 = $33.25
Full Equation:
50.00 - [(4 × 1.25) + (2 × 3.50) + 4.75]
= 50.00 - [5.00 + 7.00 + 4.75]
= 50.00 - 16.75
= 33.25
Answer: Maria has $33.25 left
Example 2:
"A rectangular garden is 12.5 meters long and 8.4 meters wide. If fencing costs $6.50 per meter, how much will it cost to fence the entire garden?"
Step 1: Find the perimeter (distance around)
Perimeter = 2 × (length + width)
= 2 × (12.5 + 8.4)
= 2 × 20.9
= 41.8 meters
Step 2: Calculate total cost
Cost = 41.8 × $6.50
= $271.70
Full Equation:
[2 × (12.5 + 8.4)] × 6.50
= [2 × 20.9] × 6.50
= 41.8 × 6.50
= 271.70
Answer: The fencing will cost $271.70
Example 3:
"A pizza parlor charges $12.75 for a large pizza plus $1.50 for each topping. If 3 friends split the cost of a pizza with 4 toppings equally, how much does each person pay?"
Step 1: Find cost of toppings
4 × $1.50 = $6.00
Step 2: Find total pizza cost
$12.75 + $6.00 = $18.75
Step 3: Divide by 3 friends
$18.75 ÷ 3 = $6.25
Full Equation:
[12.75 + (4 × 1.50)] ÷ 3
= [12.75 + 6.00] ÷ 3
= 18.75 ÷ 3
= 6.25
Answer: Each person pays $6.25
4. Equations with Mixed Operations: True or False
What Does This Mean?
You must determine if an equation is TRUE or FALSE by evaluating both sides and comparing them.
TRUE: Both sides equal the same value
FALSE: The sides equal different values
Steps to Determine True or False
Step 1: Look at the equation (it has an = sign)
Step 2: Evaluate the LEFT side using order of operations
Step 3: Evaluate the RIGHT side using order of operations
Step 4: Compare the two answers
Step 5: If they're equal → TRUE; if different → FALSE
Important Reminder
Always use PEMDAS/BODMAS to evaluate each side! The order of operations must be followed on BOTH sides of the equation.
Examples
Example 1: Is this equation TRUE or FALSE?
3.5 + 2.0 × 4.0 = 11.5
Evaluate LEFT side:
3.5 + 2.0 × 4.0
Multiply first: 2.0 × 4.0 = 8.0
Then add: 3.5 + 8.0 = 11.5
Evaluate RIGHT side:
11.5
Compare:
Left side = 11.5
Right side = 11.5
11.5 = 11.5 ✓
Answer: TRUE
Example 2: Is this equation TRUE or FALSE?
(10.0 - 4.5) × 2.0 = 10.0
Evaluate LEFT side:
(10.0 - 4.5) × 2.0
Parentheses first: 10.0 - 4.5 = 5.5
Then multiply: 5.5 × 2.0 = 11.0
Evaluate RIGHT side:
10.0
Compare:
Left side = 11.0
Right side = 10.0
11.0 ≠ 10.0 ✗
Answer: FALSE
Example 3: Is this equation TRUE or FALSE?
15.6 ÷ 2.0 + 3.2 = 7.8 × 1.5 - 3.9
Evaluate LEFT side:
15.6 ÷ 2.0 + 3.2
Divide first: 15.6 ÷ 2.0 = 7.8
Then add: 7.8 + 3.2 = 11.0
Evaluate RIGHT side:
7.8 × 1.5 - 3.9
Multiply first: 7.8 × 1.5 = 11.7
Then subtract: 11.7 - 3.9 = 7.8
Compare:
Left side = 11.0
Right side = 7.8
11.0 ≠ 7.8 ✗
Answer: FALSE
Example 4: Is this equation TRUE or FALSE?
20.0 - 5.0 × 2.0 = (20.0 - 5.0) × 2.0
Evaluate LEFT side:
20.0 - 5.0 × 2.0
Multiply first: 5.0 × 2.0 = 10.0
Then subtract: 20.0 - 10.0 = 10.0
Evaluate RIGHT side:
(20.0 - 5.0) × 2.0
Parentheses first: 20.0 - 5.0 = 15.0
Then multiply: 15.0 × 2.0 = 30.0
Compare:
Left side = 10.0
Right side = 30.0
10.0 ≠ 30.0 ✗
Answer: FALSE
Note: This example shows how parentheses change everything! Without parentheses, we multiply first. With parentheses, we subtract first.
Quick Reference Guide
Order of Operations (PEMDAS)
Step | Operation | What to Do |
---|---|---|
1st | Parentheses ( ) | Solve everything inside parentheses first |
2nd | Exponents/Powers | Solve powers and square roots |
3rd | × and ÷ | Work from LEFT to RIGHT |
4th | + and − | Work from LEFT to RIGHT |
💡 Important Tips to Remember
✓ Always follow the order of operations (PEMDAS/BODMAS)
✓ Parentheses are your best friend - they tell you what to do first
✓ Multiplication and Division are equal - do whichever comes first from left to right
✓ Addition and Subtraction are equal - do whichever comes first from left to right
✓ In word problems, underline important numbers and circle key words
✓ For multi-step problems, solve one step at a time and write it down
✓ For true/false equations, solve both sides separately before comparing
✓ Check your answer - does it make sense for the problem?
✓ Always include units in your final answer (dollars, meters, etc.)
⚠️ Common Mistakes to Avoid
❌ Mistake #1: Working from left to right for ALL operations
Example: 5 + 3 × 2 = 16 ✗ (Wrong!)
✓ Correct: 5 + 3 × 2 = 5 + 6 = 11
❌ Mistake #2: Ignoring parentheses
Example: (8 - 3) × 2 = 8 - 6 = 2 ✗ (Wrong!)
✓ Correct: (8 - 3) × 2 = 5 × 2 = 10
❌ Mistake #3: Doing addition before multiplication
Example: 2.5 + 1.5 × 4 = 4.0 × 4 = 16 ✗ (Wrong!)
✓ Correct: 2.5 + 1.5 × 4 = 2.5 + 6.0 = 8.5
❌ Mistake #4: Forgetting to align decimals
✓ Tip: When adding or subtracting, line up the decimal points!
📝 Practice Strategy
Step 1: Master Each Operation Separately
Make sure you're comfortable with adding, subtracting, multiplying, and dividing decimals before mixing them.
Step 2: Practice Order of Operations
Start with simple problems with 2-3 operations, then work up to more complex ones.
Step 3: Work on Word Problems
Read carefully, identify what you're looking for, and decide which operations to use.
Step 4: Try Multi-Step Problems
Break complex problems into smaller steps and solve one at a time.
Step 5: Check Your Work
Always ask yourself: "Does my answer make sense?"
Master Mixed Operations with Decimals! 🎯
Practice daily and always follow PEMDAS - you've got this!