Cogito
Grade 1 Math · Chapter 8 · Lesson 7
Word Problems Within 40
Find the missing part as well as the whole.
10 problems · about 14 minutes · 1.OA.A.1
What this lesson teaches
The child solves add-to, take-from, and put-together problems within 40, including problems with an unknown part.
- Some stories hide the whole. Add the parts.
- Some stories hide a part. Take the known part away.
- The diagram tells you which one it is.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — 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.
Review — Adding Ones Without Making a New Ten: 31 + 6 = ?
Answer 37
Why 1 one and 6 ones is 7 ones.
Warm Up
Straightforward practice. Get the method working first.
3 problemsWhole 35, one part 15. Other part?
Answer 20
Why 35 − 15 = 20.
You know both parts. What do you do?
Answer Put them together.
Why Two known parts make the whole.
Whole 30, one part 10. Other part?
Answer 20
Why 30 take away 10.
Build It Up
The same ideas with more to keep track of.
1 problemParts 16 and 13. What is the whole?
Answer 29
Why Tens with tens.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsWhole 28, one part 8. Other part?
Answer 20
Why 28 take away 8.
At the Library: 25 books in all. 15 are red. How many are not red?
Answer 10 books
Why 25 − 15 = 10.
On the Bus: 14 children get on. Then 12 more. How many in all?
Answer 26 children
Why 14 + 12 = 26.