Cogito
Grade 2 Math · Chapter 6 · Lesson 4
Rows and Columns
An array is equal groups lined up neatly.
10 problems · about 12 minutes · 2.OA.C.4
What this lesson teaches
The child describes a rectangular array by its rows and columns and finds the total.
- An array is equal groups in rows and columns.
- Rows go across, columns go down.
- 3 rows of 4 and 4 rows of 3 both give 12.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — 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.
4 problems3 rows of 5. How many in all?
Answer 15
Why 3 rows of 5 is 15.
Does 3 rows of 4 give the same total as 4 rows of 3?
Answer Yes. Both are 12.
Why The same objects are arranged a different way.
3 rows of 3. How many in all?
Answer 9
Why 3 + 3 + 3.
5 rows of 2. How many in all?
Answer 10
Why 2 five times.
Build It Up
The same ideas with more to keep track of.
2 problems2 rows of 4. How many in all?
Answer 8
Why 4 + 4.
4 rows of 4. How many in all?
Answer 16
Why 4 four times.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Egg Box: An egg box has 2 rows of 5. How many eggs does it hold?
Answer 10 eggs
Why 2 rows of 5 is 10.
The Seating Plan: A room has 4 rows of 5 chairs. How many chairs?
Answer 20 chairs
Why 4 rows of 5 is 20.