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Subject: Mathematics
Semester: 1
Period: 3
Week: 14
School Name:
Teacher’s Name:
Subject: Mathematics
Grade Level: Grade 5
Date: Week 14
Lesson Duration: 45 minutes
Week & Period: Week 14, Period 3
Topic: Fractions
Sub-topic: Adding & Subtracting Fractions (Unlike Denominators)
Learning Objectives
By the end of the lesson, students should be able to:
- Find the Least Common Denominator (LCD) of fractions
- Add fractions with unlike denominators
- Subtract fractions with unlike denominators
- Add and subtract mixed numbers with unlike denominators
Previous Knowledge
Students already know how to add and subtract fractions with like denominators
Instructional Materials
Mathematics textbook for Grade 5
Lesson Development – ABC Model
A – Anticipation (Warm-up / Starter)
Time: 5–10 minutes
Teacher writes 1/2 + 1/3 on the board and asks: “Can we add directly like before?” Learners attempt and discover denominators are different.
B – Building Knowledge (Main Lesson Body)
Time: 25–30 minutes
**Definition:**Fractions with unlike denominators are fractions that do not share the same bottom number. Before these fractions can be added or subtracted, they must be changed into equivalent fractions with a common denominator—specifically, the Least Common Denominator (LCD). The LCD is the least common multiple (LCM) of the original denominators. Once the fractions are rewritten with the same denominator, you can add or subtract the numerators, keep the common denominator, and simplify the result if necessary.
Examples:
1. 2/3+3/4
Step 1: Find LCD of 3 and 4 → 12
Step 2: Convert both fractions: 2/3=8/12, 3/4=9/12
Step 3: Add: 8/12+9/12=17/12=1 5/12
2. 5/6−1/4
LCD of 6 and 4 = 12 → 5/6=10/12, 1/4=3/12
Subtract: 10/12−3/12=7/12.
- 2 1/2+3 2/3
Convert to improper fractions: 5/2+11/3
LCD of 2 and 3 = 6 → 5/2=15/6, 11/3=22/6
Add: 15/6+22/6=37/6=6 1/6
**Learners’ Activities (Expanded):**Students use flashcards with different denominators and practice matching pairs that can be aligned with a common denominator. For example, they match 2/5 and 3/10, then write equivalent fractions with LCD 10.Students work with LCM charts to find the least common multiples of different numbers. They practice rewriting unlike fractions into like ones using multiplication. Using colored paper strips or fraction circles, students visually compare and build equivalent fractions (e.g., showing that 2/3 = 8/12 by comparing sizes).In pairs or groups, students are given sets of problems that involve identifying LCDs, converting fractions, performing the operation, and simplifying. This includes both proper and mixed numbers. They also play interactive games like “LCD Match-up”, where they find fractions with the same LCD and pair them to solve.
**Assessment Checks:**Teacher conducts quick oral quizzes such as:
– “What is the LCD of 2/5 and 3/10?” (Answer: 10)
– “Convert 2/5 and 3/10 to have like denominators.”
– “Solve 4/5−2/3”
Step 1: LCD = 15
Step 2: 4/5=12/15, 2/3=10/15
Answer: 12/15−10/15=2/15
– “Solve 1 1/2+ 2/31” → Convert and add.
Students also complete mini check-for-understanding worksheets or exit slips with 3–5 problems involving LCD, conversion, operation, and simplification.
**Notes (Expanded & Detailed):**Understanding how to add and subtract fractions with unlike denominators is essential for solving real-world problems involving parts of a whole—such as recipes, distances, time, and measurements. The Least Common Denominator (LCD) is crucial because it creates a shared reference point for comparing or combining the fractions. Learners must remember that the denominators must be the same before performing any addition or subtraction. If not, the fractional parts are unequal and cannot be directly operated on. Once fractions are aligned, add or subtract the numerators only, keep the denominator unchanged, and simplify the result if necessary (e.g., reduce to lowest terms or convert improper fractions to mixed numbers). This foundational skill also prepares students for solving equations and for more complex operations involving rational numbers in higher grades.C – Consolidation (Conclusion & Assessment)
Time: 5–10 minutes
Summary: Teacher emphasizes that denominators must be made equal before operation.
Evaluation Method (Expanded):
Exit slip/quiz:
Add: 2/5 + 3/10
Subtract: 7/8 – 5/12
Teacher will collect slips and provide oral feedback.
Assignment (Expanded):
Solve:
1/3 + 1/6
5/12 + 7/18
2 3/5 – 1 1/2
Follow-up Activity:
Learners prepare at least two examples of fraction problems with unlike denominators to solve in next class.
Differentiation / Inclusive Strategies
Support weaker learners with step-by-step LCD finding. Challenge advanced learners with larger denominators.
Teacher’s Reflection (After Class)
What worked well? ___________________________________________
What needs improvement? ____________________________________
Students’ engagement level: ☑ High ☑ Medium ☑ Low