Cogito
Grade 3 Math · Chapter 4 · Lesson 2
Area by Multiplying
Rows and columns again, so you can multiply.
10 problems · about 12 minutes · 3.MD.C.7
What this lesson teaches
The child finds the area of a rectangle by multiplying its side lengths.
- The squares in a rectangle form an array.
- So area is width times height.
- The answer is in square units.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — What Area Is: A rectangle 7 across and 3 down. What is its area?
Answer 21
Why The area is 21 square units.
Review — Two-Step Problems With a Letter: 8 × 5 − 14 = ?
Answer 26
Why 8 × 5 = 40, and 40 − 14 = 26.
Warm Up
Straightforward practice. Get the method working first.
4 problemsA rectangle 8 by 7. What is its area?
Answer 56
Why The area is 56 square units.
Why can you multiply to find an area?
Answer The squares form an array of rows and columns.
Why Equal rows are exactly what multiplication counts.
A rectangle 7 by 6. What is its area?
Answer 42
Why 7 × 6.
A rectangle 8 by 5. What is its area?
Answer 40
Why 8 × 5.
Build It Up
The same ideas with more to keep track of.
2 problemsA square 6 by 6. What is its area?
Answer 36
Why 6 × 6.
A rectangle 9 by 3. What is its area?
Answer 27
Why 9 × 3.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Rug: A rug is 6 metres by 4 metres. What is its area?
Answer 24 square metres
Why The area is 24 square metres.
The Poster: A poster is 9 cm by 7 cm. What is its area?
Answer 63 square cm
Why The area is 63 square centimetres.