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Grade 5 Math Lab: The Bridge to Algebra FREE
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Adding & Subtracting Unlike Fractions
Learning Objectives
- Find common denominators
- Create equivalent fractions
- Add and subtract fractions with unlike denominators
- Simplify fraction results
Key Concepts
Unlike Fractions
Fractions with different denominators that need a common denominator to add
Common Denominator
A shared denominator that lets us combine fractions
Least Common Multiple (LCM)
The smallest number that is a multiple of both denominators
Equivalent Fractions
Fractions that represent the same value (1/2 = 2/4 = 3/6)
Theory
You can't add fractions with different denominators directly - it's like adding apples and oranges! First, convert them to the same "unit" (denominator).
**Finding a Common Denominator:**
For 1/2 + 1/3:
- Multiples of 2: 2, 4, **6**, 8, 10...
- Multiples of 3: 3, **6**, 9, 12...
- LCM = 6
**Converting to Equivalent Fractions:**
- 1/2 = ?/6 → multiply both by 3 → 3/6
- 1/3 = ?/6 → multiply both by 2 → 2/6
**Now Add:**
3/6 + 2/6 = 5/6
**Visual Model (Fraction Bars):**
When you slice both bars into the same number of pieces, you can see how they combine!
Examples
1/4 + 2/3
Solution: LCM=12: 3/12 + 8/12 = 11/12
5/6 - 1/4
Solution: LCM=12: 10/12 - 3/12 = 7/12
2/5 + 3/10
Solution: LCM=10: 4/10 + 3/10 = 7/10
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Knowledge Check
Test your understanding of Equivalence Slicer!