Operations with Measurements

Grade 4 · Mathematics

Semester 2 | Period 5 | Week 28

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Subject: Mathematics

Semester: 2

Period: 5

Week: 28

School Name:
Teacher’s Name:
Subject: Mathematics
Grade Level: Grade 4
Date: Week 28
Lesson Duration: 45 minutes
Week & Period: Week 28, Period 5
Topic: Operations with Measurements
Sub-topic: Addition and subtraction of length and weight

Learning Objectives
By the end of the lesson, students should be able to:

  1. Convert subunits of length and weight in the metric system.
  2. Perform addition and subtraction of measurements.
  3. Solve word problems involving measurement.

Previous Knowledge
Students already know how to measure and convert simple metric units.

Instructional Materials
Mathematics textbook for Grade 4, rulers, scales, chalkboard.

Lesson Development – ABC Model
A – Anticipation (Warm-up / Starter)
Time: 5–10 minutes
Teacher asks: “If I have 2 meters of ribbon and add another 50 cm, how long will I have in total?”

B – Building Knowledge (Main Lesson Body)
Time: 25–30 minutes

🔍 Key Concepts (Expanded)

This lesson focuses on performing operations (addition and subtraction) with metric units of length and mass, and understanding how to convert between units when necessary. It also introduces solving real-world word problems involving metric measurements.

📐 Essential Rules & Conversions

✅ Metric Conversions (Base-10 system makes these simple):

  • Length:
    • 100 cm = 1 m
    • To convert cm to m: divide by 100
      (e.g., 150 cm = 1 m 50 cm)
  • Mass:
    • 1,000 g = 1 kg
    • To convert grams to kilograms: divide by 1,000
      (e.g., 2,500 g = 2 kg 500 g)

✅ Before adding or subtracting, convert all values to the same units or to mixed form (e.g., meters and centimeters, kilograms and grams).

 

🧠 Examples (Expanded & Explained)

  1. Conversion Example:

Convert 150 cm to meters
➤ 150 cm ÷ 100 = 1 meter and 50 centimeters
✅ Answer: 1 m 50 cm

 

  1. Addition Example – Length:

Add: 2 m 30 cm + 1 m 40 cm
Step 1: Add meters → 2 m + 1 m = 3 m
Step 2: Add centimeters → 30 cm + 40 cm = 70 cm
✅ Final Answer: 3 m 70 cm

 

  1. Subtraction Example – Mass:

Subtract: 5 kg – 2 kg 500 g
Step 1: Convert 5 kg into 4 kg 1000 g (to make subtraction easier)
Step 2: Subtract grams → 1000 g – 500 g = 500 g
Step 3: Subtract kilograms → 4 kg – 2 kg = 2 kg
✅ Final Answer: 2 kg 500 g

 

  1. Word Problem Example:

A boy walked 2 km in the morning and 3 km in the evening. How far did he walk in total?
Step 1: Add the distances → 2 km + 3 km = 5 km
✅ Answer: 5 kilometers

 

🧍‍♀️ Learners’ Activities (Expanded & Interactive)

  1. Group Problem-Solving Stations
  • Station 1: Addition of Length
    • Students solve problems like:
      • 1 m 45 cm + 2 m 60 cm
      • 3 m 90 cm + 1 m 15 cm
    • Use rulers and measuring tapes to visualize problems.
  • Station 2: Subtraction of Mass
    • Students weigh classroom items with scales (e.g., bags of rice, books).
    • Solve problems like:
      • 5 kg – 2 kg 750 g
      • 3 kg – 1 kg 500 g
  • Station 3: Word Problems & Estimations
    • Read and solve word problems involving distance, weight, or liquid.
    • Example:
      "Maria poured 300 mL of juice into a glass and 200 mL into another. How much juice did she pour in total?"
  1. Conversion Race Game
  • Students race to convert measurements correctly:
    • 1,200 g = ?
    • 350 cm = ?
    • 2 kg 300 g = ? g
    • 3 m 80 cm = ? cm

 

✅ Assessment Checks (Expanded)

Oral/Quick Checks:

  1. “Add 2 m 50 cm and 3 m 20 cm.”
    ➤ 2 m + 3 m = 5 m
    ➤ 50 cm + 20 cm = 70 cm
    ✅ Answer: 5 m 70 cm
  2. “How many grams are in 2 kilograms?”
    ✅ 2,000 g
  3. “What is 1 m 75 cm in centimeters?”
    ➤ (1 × 100) + 75 = ✅ 175 cm
  4. “Subtract: 4 kg – 1 kg 500 g.”
    ➤ Answer: 2 kg 500 g

 

📝 Teacher Notes (Expanded & Detailed)

  • Stress the importance of conversions before operations:
    • Students often try to add cm to m or g to kg directly. Demonstrate how mixing units leads to errors.
    • Model using place value to line up units (kg with kg, g with g).
  • Use visual aids and real-life context:
    • Show what 1 meter and 1 kilogram look like.
    • Bring real items: water bottles, small weights, metersticks, food packaging.
  • Teach mixed-unit operations explicitly:
    • e.g., 3 kg 750 g + 2 kg 500 g →
      Add grams: 750 + 500 = 1,250 g = 1 kg 250 g
      Add kilograms: 3 + 2 = 5 kg
      Total = 6 kg 250 g
  • Reinforce metric vocabulary:
    • Write out full terms and abbreviations:
      centimeter (cm), meter (m), gram (g), kilogram (kg)

 

📘 Optional Homework or Extension

  • Practice Worksheet with:
    • Conversion exercises
    • Mixed addition and subtraction problems
    • 2–3 real-world word problems
  • "Metric in My Life" Activity:
    • Students list and estimate the measurements of 3 items they use at home (e.g., cereal box mass, shoe length, water bottle capacity).

 

C – Consolidation (Conclusion & Assessment)
Time: 5–10 minutes
Summary: Lengths and weights can be added or subtracted after converting into the same unit.

Evaluation Method (Expanded)
Exit slip/quiz: Subtract 4 kg 500 g from 7 kg.

Assignment (Expanded)
Solve 5 word problems involving addition and subtraction of metric units.

Follow-up Activity
Students will measure household items and add/subtract their measurements.

Differentiation / Inclusive Strategies
Pair learners of mixed ability for problem-solving. Use visual aids and real objects.

Teacher’s Reflection (After Class)
What worked well? ___________________________________________
What needs improvement? ____________________________________
Students’ engagement level: ☑ High ☑ Medium ☑ Low