Cogito
Grade 2 Math · Chapter 6 · Lesson 5
Writing the Equation
Turn an array into a number sentence.
10 problems · about 12 minutes · 2.OA.C.4
What this lesson teaches
The child writes an equation expressing an array total as a sum of equal addends.
- Write the row size once for each row.
- All the addends are the same.
- That is what makes it an equal-groups equation.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Rows and Columns: 3 rows of 5. How many in all?
Answer 15
Why 3 rows of 5 is 15.
Review — Equal Groups: 5 groups of 4. How many in all?
Answer 20
Why 4 + 4 + 4 + 4 + 4 = 20.
Review — Two Equal Addends: 14 = ? + ? What is each part?
Answer 7
Why 7 + 7 = 14.
Warm Up
Straightforward practice. Get the method working first.
3 problems3 rows of 4. What is the total?
Answer 12
Why 3 rows of 4 is 12.
In the equation for an array, how many addends are there?
Answer One for each row.
Why Each row gives one addend, and they all match.
4 rows of 5. What is the total?
Answer 20
Why 5 four times.
Build It Up
The same ideas with more to keep track of.
1 problem2 rows of 3. How many addends in the equation?
Answer 2
Why One per row.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problems5 rows of 5. What is the total?
Answer 25
Why 5 five times.
The Stickers: A sheet has 3 rows of 5 stickers. How many addends are in its equation?
Answer 3
Why Three rows means three addends: 5 + 5 + 5.
The Total: What is the total for 3 rows of 5?
Answer 15 stickers
Why 3 rows of 5 is 15.