Cogito
Grade 4 Math · Chapter 7 · Lesson 8
Area and Perimeter Formulas
Two different questions about the same rectangle.
10 problems · about 16 minutes · 4.MD.A.3
What this lesson teaches
The child applies area and perimeter formulas for rectangles, including finding a missing side.
- Area is length × width. Perimeter goes round the edge.
- A missing side is found by dividing the area.
- The same perimeter can give very different areas.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
1 problemReview — Units of Measurement: 7 metres in centimetres?
Answer 700
Why 700 centimetres.
Warm Up
Straightforward practice. Get the method working first.
4 problemsArea of an 11 by 6 rectangle?
Answer 66
Why 66 square units.
Perimeter of an 11 by 6 rectangle?
Answer 34
Why 34 units.
Area of a 12 by 5 rectangle?
Answer 60
Why 12 × 5.
Perimeter of a 12 by 5 rectangle?
Answer 34
Why 12 + 5 + 12 + 5.
Build It Up
The same ideas with more to keep track of.
2 problemsArea is 72, one side is 8. How long is the other?
Answer 9
Why 72 ÷ 8.
Do two rectangles with the same perimeter always have the same area?
Answer No.
Why 1 by 11 against 6 by 6.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsThe Garden: A garden is 9 m by 7 m. What is its area, in square metres?
Answer 63 square metres
Why 63 square metres.
The Fence: The same 9 m by 7 m garden. How much fence goes all the way round?
Answer 32 metres
Why 32 metres of fence.
The Missing Side: A rectangle has an area of 54 and one side of 9. How long is the other side?
Answer 6
Why 6.