Cogito
Grade 2 Math · Chapter 2 · Lesson 8
From Ruler to Number Line
Take the object away and the ruler becomes a number line.
10 problems · about 12 minutes · 2.MD.B.6
What this lesson teaches
The child reads a number line as a length model, locating whole numbers as distances from zero.
- A number line is a ruler with nothing on it.
- A number marks its distance from 0.
- Count the spaces you move, not the marks you pass.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Length Word Problems: A 23 cm and a 19 cm strip joined. How long in all?
Answer 42
Why 23 + 19 = 42 centimetres.
Review — How Much Longer?: A 16 cm rope and an 11 cm rope. How much longer is the first?
Answer 5
Why 16 − 11 = 5 centimetres.
Review — Estimating Length: About how long is one big step?
Answer About 1 metre.
Why A big step is roughly a metre.
Warm Up
Straightforward practice. Get the method working first.
3 problemsHow far is 13 from 0 on a number line?
Answer 13
Why 13 is 13 units from 0.
On a number line, what should you count?
Answer The spaces you move.
Why Counting marks instead of spaces is how you end up one out.
Two spaces past 10 is which number?
Answer 12
Why Count on two.
Build It Up
The same ideas with more to keep track of.
1 problemOne space before 15 is which number?
Answer 14
Why Count back one.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsHow far is the 9 mark from 0?
Answer 9
Why The number is the distance.
Reading the Line: A dot sits three spaces past the 15 mark. What number is it on?
Answer 18
Why 15 and 3 more is 18.
Back From Twenty: A dot sits four spaces before the 20 mark. What number is it on?
Answer 16
Why 20 take away 4 is 16.