Cogito
Grade 2 Math · Chapter 2 · Lesson 9
Adding and Subtracting on a Number Line
A jump forward adds. A jump back takes away.
10 problems · about 14 minutes · 2.MD.B.6, 2.OA.A.1
What this lesson teaches
The child represents sums and differences within 100 as jumps on a number line.
- A forward jump adds. A backward jump takes away.
- Jump the tens first, then the ones.
- Where you land is the answer.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — From Ruler to Number Line: How far is 13 from 0 on a number line?
Answer 13
Why 13 is 13 units from 0.
Review — Length Word Problems: A 23 cm and a 19 cm strip joined. How long in all?
Answer 42
Why 23 + 19 = 42 centimetres.
Warm Up
Straightforward practice. Get the method working first.
4 problemsStart at 26 and jump forward 20. Where do you land?
Answer 46
Why 26 + 20 = 46.
Which way does a subtraction jump go?
Answer Backwards.
Why Subtracting moves you back down the line.
35 + 20 = ?
Answer 55
Why Two jumps of ten.
42 + 14 = ?
Answer 56
Why Jump 10, then 4.
Build It Up
The same ideas with more to keep track of.
2 problems60 − 30 = ?
Answer 30
Why Three jumps back of ten.
48 − 12 = ?
Answer 36
Why Back 10, then back 2.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Long Jump: Ana starts at 31 and jumps forward 20, then 5. Where does she land?
Answer 56
Why 31 + 20 + 5 = 56.
Going Back: Leo starts at 52 and jumps back 20. Where does he land?
Answer 32
Why 52 − 20 = 32.