Cogito
Grade 1 Math · Chapter 3 · Lesson 4
The Hidden Part
You can see one part. Work out the other.
10 problems · about 11 minutes · 1.OA.B.4, 1.OA.A.1
What this lesson teaches
The child solves take-apart-with-addend-unknown stories by identifying the known part within the whole.
- A whole splits into two parts.
- Knowing one part tells you the other.
- Count up from the part you know.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
5 problemsReview — Taking Away: 7 − 3 = ?
Answer 4
Why 7 − 3 = 4.
Review — Counting Up To Subtract: 9 − 7 = ?
Answer 2
Why Two hops, so the answer is 2.
Review — How Many More To Make It?: 3 + ? = 7
Answer 4
Why 3 + 4 = 7.
Review — Facts to Ten: 7 + 3 = ?
Answer 10
Why 7 + 3 = 10.
Review — Doubles and One More: 3 + 4 = ?
Answer 7
Why 3 + 3 = 6, and one more is 7.
Warm Up
Straightforward practice. Get the method working first.
3 problemsWhole 9, one part 4. What is the other part?
Answer 5
Why 4 + 5 = 9.
Whole 6, one part 1. What is the other part?
Answer 5
Why 1 + 5 = 6.
Whole 7, one part 2. What is the other part?
Answer 5
Why Count up from 2 to 7.
Build It Up
The same ideas with more to keep track of.
1 problemWhole 10, one part 6. What is the other part?
Answer 4
Why A partner to ten.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
1 problemSock Drawer: Leo has 8 socks. 3 are stripy and the rest are plain. How many are plain?
Answer 5 socks
Why 3 + 5 = 8, so 5 are plain.