Cogito
Grade 1 Math · Chapter 2 · Lesson 6
Finding the Missing Part
Work out the number that is hiding.
10 problems · about 12 minutes · 1.OA.D.8, 1.OA.C.6
What this lesson teaches
The child finds an unknown addend in equations such as 6 + ? = 9 by counting on from the known part.
- A missing part can hide anywhere in a sentence.
- Start at the part you know.
- Count up to the whole and count your hops.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — What Does Equals Mean?: What does the equals sign mean?
Answer Both sides are the same amount.
Why Equals means the same amount as. That is why 9 = 6 + 3 works too.
Review — Adding in Any Order: 3 + 5 = 8. So what is 5 + 3?
Answer 8
Why Swapping the parts never changes the whole.
Review — Counting On With Pictures: Start at 9. Count on 1. Where do you land?
Answer 10
Why 9 + 1 = 10.
Review — Counting On: 8 + 2 = ?
Answer 10
Why 8 + 2 = 10.
Warm Up
Straightforward practice. Get the method working first.
3 problems5 + ? = 9
Answer 4
Why 5 + 4 = 9.
3 + ? = 10
Answer 7
Why 3 + 7 = 10.
4 + ? = 7
Answer 3
Why Count from 4 up to 7.
Build It Up
The same ideas with more to keep track of.
1 problem6 + ? = 10
Answer 4
Why This is a partner to ten.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problems2 + ? = 9
Answer 7
Why Count from 2 up to 9.
The Bookshelf: Leo needs 8 books. He has 5 already. How many more does he need?
Answer 3 books
Why 5 + 3 = 8, so he needs 3 more.