Cogito
Grade 4 Math · Chapter 4 · Lesson 1
Factor Pairs
Every rectangle you can build from a number.
10 problems · about 14 minutes · 4.OA.B.4
What this lesson teaches
The child finds all factor pairs of a whole number up to 100.
- A factor divides a number exactly.
- Factors come in pairs, and each pair is a rectangle.
- Search from 1 upwards so none get missed.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Multistep Word Problems: 7 × 24 − 68 = ?
Answer 100
Why 7 × 24 = 168, and 168 − 68 = 100.
Review — What the Remainder Means: 35 children, buses hold 9. How many buses?
Answer 4
Why Round up to 4 buses.
Warm Up
Straightforward practice. Get the method working first.
4 problemsHow many factors does 36 have?
Answer 9
Why 36 has 9 factors, because 6 × 6 counts only once.
Is 1 a factor of every number?
Answer Yes.
Why Every number has 1 and itself as factors.
How many factors does 16 have?
Answer 5
Why 1, 2, 4, 8, 16.
How many factors does 10 have?
Answer 4
Why 1, 2, 5, 10.
Build It Up
The same ideas with more to keep track of.
2 problemsIs 7 a factor of 42?
Answer Yes. 7 × 6 = 42.
Why Count in sevens.
What is the largest factor of 30 apart from 30?
Answer 15
Why 30 ÷ 2.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Garden Beds: 24 plants in equal rows. How many different rectangles are possible?
Answer 8 rectangles
Why 24 has 8 factors, so 8 rectangles.
The Chairs: 20 chairs in rows of 6. Does that work with none left over?
Answer No. 6 is not a factor of 20.
Why 20 ÷ 6 leaves a remainder, so 6 is not a factor.