Basic Math

Mixed operations: decimals | Fifth Grade

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

OperationKey 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)

StepOperationWhat to Do
1stParentheses ( )Solve everything inside parentheses first
2ndExponents/PowersSolve 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!

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