Cogito
Grade 1 Math · Chapter 8 · Lesson 9
When the Ones Make a Ten
Sometimes the ones fill up and you need a new ten.
10 problems · about 14 minutes · 1.NBT.C.4
What this lesson teaches
The child adds two two-digit numbers whose ones compose a new ten, and performs the bundling.
- Sometimes the ones add up to ten or more.
- Bundle ten of them into a new ten.
- Then say the answer as tens and ones.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — Adding Two-Digit Numbers: 21 + 14 = ?
Answer 35
Why 3 tens and 5 ones is 35.
Review — Word Problems Within 40: Whole 35, one part 15. Other part?
Answer 20
Why 35 − 15 = 20.
Review — Tape Diagrams for Stories: Parts of 13 and 12. What is the whole?
Answer 25
Why 13 + 12 = 25.
Review — Making the Next Ten: 29 + 5 = ?
Answer 34
Why 30 and 4 more is 34.
Warm Up
Straightforward practice. Get the method working first.
3 problems16 + 17 = ?
Answer 33
Why 2 tens and 13 ones becomes 3 tens and 3 ones.
When do you need a new ten?
Answer When the ones reach ten.
Why Only when the loose ones reach ten.
15 + 17 = ?
Answer 32
Why 5 and 7 is 12.
Build It Up
The same ideas with more to keep track of.
1 problem19 + 13 = ?
Answer 32
Why 9 and 3 is 12.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problems14 + 12 = ?
Answer 26
Why 4 and 2 is only 6.
Two Jars: 17 buttons in one jar and 15 in another. How many?
Answer 32 buttons
Why 7 and 5 is 12, so one more ten is made.