Lesson 5.3 · Knowing decimetres
Hua's Classroom for Shanghai Maths — One Lesson One Exercise (English edition, pages 112–114).
Lesson Alignment
How this Shanghai Maths lesson connects to learning goals, Common Core, and Eureka Math.
Learning Objectives
Students will be able to:
- 01Know $1\ \text{dm} = 10\ \text{cm}$ and relate to m / km / mm.
- 02Choose equal lengths among mixed units.
- 03Estimate heights and solve rope × times problems.
Common Core Standards
| Code | Standard (focus for this lesson) |
|---|---|
| 3.MD.A.2 | Measure/estimate lengths; solve problems. |
| 3.MD.B.4 | *(related)* Generate measurement data. |
| 4.MD.A.1 | *(preview)* Know relative sizes of km, m, cm. |
| 4.MD.A.1 | *(preview)* Relative sizes of metric units. |
Eureka Math Correspondence
| Shanghai Maths | Focus | Eureka Math |
|---|---|---|
| dm | Between cm and m | Measurement fluency |
Core Concepts
Place the decimetre on the metric ladder and compare carefully.
Decimetre
Metric Ladder
Watch traps: $30\ \text{cm}\neq3\ \text{mm}$; $3\ \text{m}\ 6\ \text{cm}=306\ \text{cm}$ (not $306\ \text{dm}$).
Estimate & MCQ
Order lengths; estimate a person’s height; rope $3\ \text{m}\ 5\ \text{dm}$ used 8 times.
Key Terms & Definitions (Reference)
Quick glossary for this lesson.
| Term | Definition |
|---|---|
| Decimetre (dm) | $1\ \text{dm}=10\ \text{cm}=0.1\ \text{m}$. |
| Millimetre (mm) | $10\ \text{mm}=1\ \text{cm}$ (comparison traps). |
Key Answers
Quick reference for this lesson’s exercise answers.
1. Fill in — $10$; $6$; $2$; $60\,\mathrm{dm}=600\,\mathrm{cm}=6000\,\mathrm{mm}$; $40$; $60$; $30\,000$; $29$; $504$.
2. Units — dm; mm; cm; m; cm; km; m; m.
3. $172\,\mathrm{cm}$; $1\,\mathrm{m}\,59\,\mathrm{cm}$; $4\,\mathrm{m}\,83\,\mathrm{cm}$; ruler $\approx1\,\mathrm{dm}$, stick $\approx7\,\mathrm{cm}\,0\,\mathrm{mm}$; Pencil 2 is $15\,\mathrm{mm}$ longer.
4. Compare — >; =; >; >; <; >; >; =; >; <.
5. Order — $5\,\mathrm{m}\,40\,\mathrm{cm}<542\,\mathrm{cm}<55\,\mathrm{dm}<450\,\mathrm{dm}$;\; $1\,\mathrm{km}\,210\,\mathrm{m}<2\,\mathrm{km}<2200\,\mathrm{m}<21\,000\,\mathrm{m}$.
6. MC — C; C; C; D.
7. $80\,\mathrm{km}$, $80\,000\,\mathrm{m}$;\; $145\,\mathrm{cm}$;\; $28\,\mathrm{m}$.
8. $48\,\mathrm{dm}$;\; $602\,\mathrm{cm}$ and $398\,\mathrm{cm}$.