Mixed Operations: Fractions & Mixed Numbers
Complete Notes & Formulae for 5th Grade Math
📚 Key Definitions
Proper Fraction: A fraction where the numerator is less than the denominator.
Example: $\frac{3}{4}$, $\frac{5}{8}$, $\frac{2}{7}$
Improper Fraction: A fraction where the numerator is greater than or equal to the denominator.
Example: $\frac{7}{4}$, $\frac{11}{3}$, $\frac{9}{9}$
Mixed Number: A whole number and a proper fraction combined.
Example: $2\frac{3}{4}$, $5\frac{1}{2}$, $1\frac{5}{8}$
🔄 Converting Between Forms
Mixed Number → Improper Fraction
Formula:
$$a\frac{b}{c} = \frac{(a \times c) + b}{c}$$
Steps:
- Multiply the whole number by the denominator
- Add the numerator to the result
- Place the result over the original denominator
Example:
$2\frac{3}{5} = \frac{(2 \times 5) + 3}{5} = \frac{10 + 3}{5} = \frac{13}{5}$
Improper Fraction → Mixed Number
Formula:
$$\frac{a}{b} = q\frac{r}{b}$$
(where $q$ is the quotient and $r$ is the remainder when dividing $a$ by $b$)
Steps:
- Divide the numerator by the denominator
- The quotient becomes the whole number
- The remainder becomes the new numerator
- Keep the same denominator
Example:
$\frac{17}{5} = 3\frac{2}{5}$ (because $17 \div 5 = 3$ remainder $2$)
➕ Adding Fractions & Mixed Numbers
Adding Fractions with Like Denominators
Formula:
$$\frac{a}{c} + \frac{b}{c} = \frac{a + b}{c}$$
Steps:
- Add the numerators
- Keep the same denominator
- Simplify if possible
Example:
$\frac{2}{7} + \frac{3}{7} = \frac{2 + 3}{7} = \frac{5}{7}$
Adding Fractions with Unlike Denominators
Formula:
$$\frac{a}{b} + \frac{c}{d} = \frac{(a \times d) + (c \times b)}{b \times d}$$
Steps:
- Find the least common denominator (LCD)
- Convert fractions to equivalent fractions with LCD
- Add the numerators
- Keep the common denominator
- Simplify if possible
Example:
$\frac{1}{4} + \frac{1}{3} = \frac{3}{12} + \frac{4}{12} = \frac{7}{12}$
Adding Mixed Numbers
Steps:
- Method 1: Convert to improper fractions, add, then convert back
- Method 2: Add whole numbers and fractions separately
Example (Method 2):
$2\frac{1}{4} + 1\frac{2}{4} = (2 + 1) + (\frac{1}{4} + \frac{2}{4}) = 3 + \frac{3}{4} = 3\frac{3}{4}$
➖ Subtracting Fractions & Mixed Numbers
Subtracting Fractions with Like Denominators
Formula:
$$\frac{a}{c} - \frac{b}{c} = \frac{a - b}{c}$$
Steps:
- Subtract the numerators
- Keep the same denominator
- Simplify if possible
Example:
$\frac{5}{8} - \frac{2}{8} = \frac{5 - 2}{8} = \frac{3}{8}$
Subtracting Fractions with Unlike Denominators
Formula:
$$\frac{a}{b} - \frac{c}{d} = \frac{(a \times d) - (c \times b)}{b \times d}$$
Steps:
- Find the least common denominator (LCD)
- Convert fractions to equivalent fractions with LCD
- Subtract the numerators
- Keep the common denominator
- Simplify if possible
Example:
$\frac{3}{4} - \frac{1}{3} = \frac{9}{12} - \frac{4}{12} = \frac{5}{12}$
Subtracting Mixed Numbers (with Borrowing)
Steps:
- If the fraction part of the first number is smaller, borrow 1 from the whole number
- Convert the borrowed 1 to a fraction with the same denominator
- Add it to the fraction part
- Subtract whole numbers and fractions separately
Example:
$5\frac{1}{4} - 2\frac{3}{4} = 4\frac{5}{4} - 2\frac{3}{4} = (4-2) + (\frac{5}{4} - \frac{3}{4}) = 2\frac{2}{4} = 2\frac{1}{2}$
✖️ Multiplying Fractions & Mixed Numbers
Multiplying Fractions
Formula:
$$\frac{a}{b} \times \frac{c}{d} = \frac{a \times c}{b \times d}$$
Steps:
- Multiply the numerators together
- Multiply the denominators together
- Simplify the result if possible
- Tip: You can simplify before multiplying by canceling common factors
Example:
$\frac{2}{3} \times \frac{3}{5} = \frac{2 \times 3}{3 \times 5} = \frac{6}{15} = \frac{2}{5}$
Multiplying Mixed Numbers
Steps:
- Convert all mixed numbers to improper fractions
- Multiply the numerators together
- Multiply the denominators together
- Simplify and convert back to a mixed number if needed
Example:
$2\frac{1}{2} \times 1\frac{1}{3} = \frac{5}{2} \times \frac{4}{3} = \frac{20}{6} = \frac{10}{3} = 3\frac{1}{3}$
Multiplying Fractions by Whole Numbers
Formula:
$$n \times \frac{a}{b} = \frac{n \times a}{b}$$
Steps:
- Multiply the whole number by the numerator
- Keep the same denominator
- Simplify if possible
Example:
$4 \times \frac{2}{3} = \frac{4 \times 2}{3} = \frac{8}{3} = 2\frac{2}{3}$
➗ Dividing Fractions & Mixed Numbers
Dividing Fractions (Keep, Change, Flip)
Formula:
$$\frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \times \frac{d}{c} = \frac{a \times d}{b \times c}$$
Steps (Keep, Change, Flip):
- Keep the first fraction the same
- Change the division sign to multiplication
- Flip the second fraction (find its reciprocal)
- Multiply the fractions
- Simplify if possible
Example:
$\frac{2}{3} \div \frac{4}{5} = \frac{2}{3} \times \frac{5}{4} = \frac{10}{12} = \frac{5}{6}$
Dividing Mixed Numbers
Steps:
- Convert all mixed numbers to improper fractions
- Use "Keep, Change, Flip" method
- Multiply the fractions
- Simplify and convert back to a mixed number if needed
Example:
$3\frac{1}{2} \div 1\frac{3}{4} = \frac{7}{2} \div \frac{7}{4} = \frac{7}{2} \times \frac{4}{7} = \frac{28}{14} = 2$
Dividing Whole Numbers by Fractions
Formula:
$$n \div \frac{a}{b} = n \times \frac{b}{a} = \frac{n \times b}{a}$$
Steps:
- Write the whole number as a fraction ($\frac{n}{1}$)
- Use "Keep, Change, Flip" method
- Multiply and simplify
Example:
$6 \div \frac{2}{3} = \frac{6}{1} \times \frac{3}{2} = \frac{18}{2} = 9$
📝 Solving Word Problems
Step-by-Step Strategy
- Read carefully: Understand what the problem is asking
- Identify key information: Circle or underline numbers and important words
- Determine the operation: Look for keywords
- Addition: total, altogether, combined, sum, in all
- Subtraction: difference, how much more, left, remaining
- Multiplication: of, times, product, each
- Division: per, each, split, shared equally, how many groups
- Write the equation: Set up the problem with the correct operation
- Solve: Follow the rules for that operation
- Check: Does your answer make sense?
- Answer in context: Include units and write a complete sentence
Example 1: Addition Word Problem
Problem:
Sarah walked $\frac{3}{4}$ mile in the morning and $1\frac{1}{2}$ miles in the evening. How far did she walk in total?
Solution:
$\frac{3}{4} + 1\frac{1}{2} = \frac{3}{4} + 1\frac{2}{4} = \frac{3}{4} + \frac{6}{4} = \frac{9}{4} = 2\frac{1}{4}$ miles
Answer: Sarah walked $2\frac{1}{4}$ miles in total.
Example 2: Multiplication Word Problem
Problem:
A recipe calls for $\frac{2}{3}$ cup of sugar. If you want to make $2\frac{1}{2}$ times the recipe, how much sugar do you need?
Solution:
$\frac{2}{3} \times 2\frac{1}{2} = \frac{2}{3} \times \frac{5}{2} = \frac{10}{6} = \frac{5}{3} = 1\frac{2}{3}$ cups
Answer: You need $1\frac{2}{3}$ cups of sugar.
Example 3: Multi-Step Word Problem
Problem:
James had $4\frac{1}{2}$ pizzas. He ate $\frac{3}{4}$ of a pizza for lunch and gave $1\frac{1}{4}$ pizzas to his friend. How much pizza does he have left?
Solution:
Step 1: Find total pizza given away/eaten: $\frac{3}{4} + 1\frac{1}{4} = \frac{3}{4} + 1\frac{1}{4} = 2$ pizzas
Step 2: Subtract from original amount: $4\frac{1}{2} - 2 = 2\frac{1}{2}$ pizzas
Answer: James has $2\frac{1}{2}$ pizzas left.
📊 Quick Reference Table
Operation | Key Rule | Example |
---|---|---|
Addition | Find common denominator, add numerators | $\frac{1}{4} + \frac{1}{2} = \frac{3}{4}$ |
Subtraction | Find common denominator, subtract numerators | $\frac{3}{4} - \frac{1}{4} = \frac{2}{4} = \frac{1}{2}$ |
Multiplication | Multiply numerators, multiply denominators | $\frac{2}{3} \times \frac{3}{4} = \frac{6}{12} = \frac{1}{2}$ |
Division | Keep, Change, Flip (multiply by reciprocal) | $\frac{1}{2} \div \frac{1}{4} = \frac{1}{2} \times \frac{4}{1} = 2$ |
💡 Important Tips & Reminders
✓ Always convert mixed numbers to improper fractions before multiplying or dividing
✓ For addition and subtraction, you MUST have a common denominator
✓ For multiplication and division, you DON'T need a common denominator
✓ Always simplify your final answer to lowest terms
✓ Remember "Keep, Change, Flip" for division problems
✓ When borrowing in subtraction, convert 1 whole to an equivalent fraction
✓ Check your work by estimating: Does your answer make sense?
📘 Study these notes regularly and practice with word problems to master fraction operations!