Learning Objectives

By the end of this lesson, the student will be able to:

• Define perimeter as the total distance around the outside of a shape.
• Calculate the missing side length of a polygon when the total perimeter and other side lengths are known.
• Apply addition and subtraction skills to solve real-world "zoo design" problems.

Materials Needed

• Paper and pencils
• Colored markers or crayons
• A ruler (metric or imperial)
• Small toy animals (optional, for "staging" the zoo)
• "The Zoo Architect" Challenge Sheet (can be drawn on plain paper)
• String or yarn (for a hands-on visual)

1. The Hook: The Monkey Mystery (5 minutes)

Scenario: "Emergency at the City Zoo! Pip the Monkey has found a gap in his fence. The Zoo Director forgot to finish the fence because they didn't know how long the last piece of wood needed to be. They knew the total distance around the enclosure, but one side is missing! We need to become 'Zoo Architects' and use our math skills to fix the fences and keep the animals safe."

Objective Check: Today, we are going to learn how to find that 'mystery side' using what we know about perimeter.

2. "I Do": Modeling the Math (10 minutes)

The Concept: Explain that perimeter is like a giant belt around a shape. If we know how big the belt is and how long most of the sides are, we can find the missing piece.

Demonstration: Draw a rectangle on a whiteboard or paper.

• Label the top as 5cm and the bottom as 5cm.
• Label one side as 3cm.
• Put a big question mark (?) on the last side.
• Tell the student: "The Zoo Director says the total perimeter must be 16cm."

Step-by-Step Logic:

1. Add what we know: 5 + 5 + 3 = 13.
2. Find the difference: We need 16 total. 16 minus 13 equals 3.
3. The Answer: The missing fence piece is 3cm!

3. "We Do": The Lion's Den (10 minutes)

Activity: Let’s solve one together before you start your zoo design.

The Problem: The Lion’s Den is a triangle.

• Side A is 10 meters.
• Side B is 10 meters.
• The total perimeter (the whole fence) is 30 meters.
• Ask the student: "How do we find Side C?"

Guided Practice: Walk through the addition (10 + 10 = 20) and the subtraction (30 - 20 = 10) together. Have the student draw the triangle and label the sides as you talk.

4. "You Do": Zoo Architect Project (20 minutes)

Task: The student must design a 3-enclosure zoo map. For each enclosure, they must leave one side "missing" for a partner (or the teacher/parent) to solve, or solve the ones provided below.

Creative Twist: After solving the math, the student colors the enclosures and draws the animals inside!

5. Success Criteria & Assessment

How to know they've got it:

• Can the student explain that perimeter is the "outside edge"?
• Can the student correctly add the known sides together?
• Can the student subtract the sum from the total perimeter to find the "missing link"?

Formative Check: Ask, "If a shape has a perimeter of 10 and I know three sides are 2, 2, and 2, what is the last side?" (Answer: 4).

6. Differentiation

• For learners needing support: Use physical string. Measure the total length of string first, then lay it around the known sides of a drawing. The leftover string is the "missing side."
• For advanced learners: Give them a perimeter of 24 and ask them to design a 6-sided "irregular" enclosure where two sides are missing, but they must be equal in length.

7. Conclusion (5 minutes)

Recap: "You did it! The fences are fixed, and Pip the Monkey is safe inside. Today we learned that if we have a total perimeter and a few side lengths, we can be math detectives to find the missing piece."

Reflection: Ask the student: "Which animal enclosure was the hardest to build? Why?"