Cogito
Grade 1 Math · Chapter 5 · Lesson 1
Adding Three Numbers
Look for two that make ten first.
10 problems · about 12 minutes · 1.OA.A.2, 1.OA.B.3
What this lesson teaches
The child adds three addends by finding a pair that makes ten and adding it first.
- You can add three numbers.
- Look for two that make ten first.
- Ten and something is always easy.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — Counting to Twenty and Back: What comes after 18?
Answer 19
Why 19 comes after 18.
Review — One More, One Less to Twenty: One more than 11?
Answer 12
Why One more than 11 is 12.
Review — Breaking Teen Numbers Apart: 12 is 10 and what?
Answer 2
Why 12 is 10 and 2.
Review — Writing Teen Numbers: In 16, how many ones are there?
Answer 6
Why 16 is one ten and 6 ones.
Warm Up
Straightforward practice. Get the method working first.
3 problems3 + 7 + 5 = ?
Answer 15
Why 3 + 7 = 10, then 10 + 5 = 15.
2 + 6 + 8 = ?
Answer 16
Why 2 + 8 = 10, then 10 + 6 = 16.
8 + 2 + 3 = ?
Answer 13
Why 8 and 2 make ten.
Build It Up
The same ideas with more to keep track of.
1 problem5 + 5 + 6 = ?
Answer 16
Why 5 and 5 make ten.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problems9 + 4 + 1 = ?
Answer 14
Why 9 and 1 make ten.
Three Baskets: One basket has 6 eggs, one has 4, one has 5. How many eggs in all?
Answer 15 eggs
Why 6 + 4 = 10, and 10 + 5 = 15.