Cogito
Grade 1 Math · Chapter 8 · Lesson 4
Adding Ones Without Making a New Ten
Add a small number when the ones still fit.
10 problems · about 11 minutes · 1.NBT.C.4
What this lesson teaches
The child adds a one-digit number to a two-digit number when the ones do not reach ten.
- Ones join the ones. Tens stay as they are.
- 23 + 4 = 27.
- This works while the ones stay under ten.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — Adding Tens to Any Number: 16 + 20 = ?
Answer 36
Why 1 ten and 2 tens is 3 tens, with 6 ones.
Review — Subtracting Tens From Tens: 30 − 20 = ?
Answer 10
Why One ten is left, which is 10.
Review — Adding Tens to Tens: 20 + 10 = ?
Answer 30
Why 2 tens and 1 ten is 3 tens.
Review — One More, One Less, Ten More, Ten Less: Ten less than 34 is?
Answer 24
Why 3 tens became 2 tens.
Warm Up
Straightforward practice. Get the method working first.
3 problems31 + 6 = ?
Answer 37
Why 1 one and 6 ones is 7 ones.
Which part changes in 22 + 3?
Answer The ones.
Why 3 joins the ones, so only the ones change.
32 + 5 = ?
Answer 37
Why 2 and 5 more.
Build It Up
The same ideas with more to keep track of.
1 problem14 + 3 = ?
Answer 17
Why 4 and 3 more.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problems25 + 4 = ?
Answer 29
Why 5 and 4 more.
More Shells: Ana has 21 shells. She finds 5 more. How many now?
Answer 26 shells
Why 21 + 5 = 26.