Chapter 1 · Revising and improving
Lesson 1.4 · Square decimetres
Hua's Classroom for Shanghai Maths — One Lesson One Exercise (English edition, pages 10–12).
Lesson Alignment
How this Shanghai Maths lesson connects to learning goals, Common Core, and Eureka Math.
Learning Objectives
Students will be able to:
- 01Understand 1 dm² as a square with side 1 dm. (Question 1)
- 02Convert between cm² and dm² using $100\ ext{cm}^2 = 1\ ext{dm}^2$. (Question 2)
- 03Compare areas in different square units. (Question 3)
- 04Solve area problems using dm². (Question 4–5)
Common Core Standards
| Code | Standard (focus for this lesson) |
|---|---|
| 3.MD.C.7 | Area and multiplication. |
| 3.MD.A.2 | Measure and estimate liquid volumes and masses (related metric sense). |
Eureka Math Correspondence
| Shanghai Maths | Focus | Eureka Math |
|---|---|---|
| Q1 | Define dm² | G3 M4 / M2 metric |
| Q2 | cm² ↔ dm² | G3 M4 |
| Applications | Desk / tile areas | G3 M4 application |
Core Concepts
Square decimetre (dm²) sits between cm² and m² on the metric area ladder.
What is dm²?
A square decimetre is the area of a $1\ ext{dm} imes 1\ ext{dm}$ square.
Since $1\ ext{dm} = 10\ ext{cm}$, one dm² equals $10 imes 10 = 100\ ext{cm}^2$.
cm² and dm²
| Convert | Rule | Example |
|---|---|---|
| cm² → dm² | Divide by 100 | $300\ ext{cm}^2 = 3\ ext{dm}^2$ |
| dm² → cm² | Multiply by 100 | $5\ ext{dm}^2 = 500\ ext{cm}^2$ |
Applications
Use dm² for medium-sized surfaces (books, trays) when cm² feels too small and m² too large.
Key Terms & Definitions (Reference)
Quick glossary for this lesson.
| Term | Definition |
|---|---|
| Square decimetre (dm²) | Area unit; side 1 dm. |
| Decimetre (dm) | 10 cm. |
| Conversion | Change units without changing size. |
Key Answers
Quick reference for this lesson’s exercise answers.
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