Cogito
Grade 2 Math · Chapter 2 · Lesson 4
The Same Object, Two Units
A smaller unit always gives a bigger number.
10 problems · about 13 minutes · 2.MD.A.2
What this lesson teaches
The child measures one object in two different units and explains why the numbers differ.
- One object can be measured in different units.
- A smaller unit gives a bigger number.
- Always say the unit with the number.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Inches and Feet: How many inches are in a foot?
Answer 12
Why 1 foot = 12 inches.
Review — Centimetres and Metres: How many centimetres are in a metre?
Answer 100
Why 1 metre = 100 centimetres.
Review — Measuring in Centimetres: Where should one end of the object go?
Answer On the 0.
Why Starting at 0 makes the far end read the length directly.
Warm Up
Straightforward practice. Get the method working first.
3 problemsWhich gives the bigger number, centimetres or metres?
Answer Centimetres.
Why Smaller unit, bigger number, same length.
Why must you say which unit you used?
Answer A number alone does not say how long.
Why The unit is half the answer.
You measure a desk in inches, then in feet. Which number is bigger?
Answer The inches number.
Why Inches are smaller than feet.
Build It Up
The same ideas with more to keep track of.
1 problemIf you swap to a bigger unit, does the number go up or down?
Answer Down. You need fewer of them.
Why Bigger units cover more each.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsA desk is 3 feet long. How many inches is that?
Answer 36
Why 12 and 12 and 12.
Two Answers: A stick is measured in centimetres and in metres. Which number is bigger?
Answer The centimetres number.
Why Centimetres are smaller, so you need more of them.
A Missing Word: Ana says her ribbon is "12". Why is that not an answer?
Answer She did not say the unit.
Why 12 centimetres and 12 inches are very different lengths.