Cogito
Grade 2 Math · Chapter 2 · Lesson 1
Measuring in Centimetres
A ruler has the units printed on already.
10 problems · about 12 minutes · 2.MD.A.1
What this lesson teaches
The child measures an object in centimetres with a ruler, aligning one end at zero.
- A ruler has the units printed on it.
- Line one end up with 0.
- The length is the distance from 0, not the tick you happen to see.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Two-Step Word Problems: 9 sweets. 5 more given. 6 eaten. How many are left?
Answer 8
Why 9 + 5 = 14, and 14 − 6 = 8.
Review — Choosing a Strategy: 9 + 7 = ?
Answer 16
Why 9 + 1 + 6 = 16.
Review — Find the Missing Number: ? + 8 = 15
Answer 7
Why 7 + 8 = 15.
Warm Up
Straightforward practice. Get the method working first.
3 problemsWhere should one end of the object go?
Answer On the 0.
Why Starting at 0 makes the far end read the length directly.
An object goes from 0 to 14 cm. How long is it?
Answer 14
Why It is 14 centimetres long.
An object goes from 0 to 7. How long is it?
Answer 7
Why Start at 0 makes it easy.
Build It Up
The same ideas with more to keep track of.
1 problemAn object goes from 3 to 9. How long is it?
Answer 6
Why Count the units from 3 up to 9.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsAn object goes from 2 to 10. How long is it?
Answer 8
Why 10 take away 2.
The Wrong Start: Leo starts a 6 cm crayon at the 2 mark. What number does the far end land on?
Answer 8 on the ruler
Why It lands on 8, but the crayon is still only 6 cm long.
Measuring a Leaf: A leaf starts at 0 and ends at 11 on the ruler. How long is the leaf?
Answer 11 cm
Why From 0 to 11 is 11 centimetres.