Cogito
Grade 2 Math · Chapter 4 · Lesson 2
Making a New Ten
When the ones fill up, bundle them.
10 problems · about 13 minutes · 2.NBT.B.5, 2.NBT.B.9
What this lesson teaches
The child adds within 100 where the ones compose a new ten, performing the bundling.
- When the ones reach ten, bundle them into a ten.
- The new ten joins the other tens.
- It is one ten, not one one.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Adding With Place Value: 23 + 41 = ?
Answer 64
Why 23 + 41 = 64.
Review — A Hundred More, A Hundred Less: A hundred more than 546 is?
Answer 646
Why 546 + 100 = 646.
Warm Up
Straightforward practice. Get the method working first.
4 problems29 + 34 = ?
Answer 63
Why 5 tens and 13 ones becomes 6 tens and 3 ones.
When you bundle ten ones, what do you get?
Answer One ten.
Why Ten ones make one ten, not one one.
46 + 27 = ?
Answer 73
Why 6 and 7 is 13.
35 + 28 = ?
Answer 63
Why 5 and 8 is 13.
Build It Up
The same ideas with more to keep track of.
2 problems42 + 31 = ?
Answer 73
Why 2 and 1 is only 3.
59 + 26 = ?
Answer 85
Why 9 and 6 is 15.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsTwo Shelves: One shelf holds 27 books and another holds 46. How many books in all?
Answer 73 books
Why 27 + 46 = 73.
Collecting: Ana has 55 shells and finds 29 more. How many does she have now?
Answer 84 shells
Why 55 + 29 = 84.