Cogito
Grade 6 Math · Chapter 3 · Lesson 6
Pulling Out a Common Factor
The distributive property, read backwards.
10 problems · about 18 minutes · 6.NS.B.4
What this lesson teaches
The child rewrites a sum of two numbers as a common factor times a sum, using the GCF.
- A sum can be rewritten as a common factor times a smaller sum.
- Divide each number by the factor to find what goes in the bracket.
- Using the greatest common factor leaves the smallest numbers inside.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Adding and Subtracting Decimals: 6.4 + 2.75 = ?
Answer 9.15
Why 9.15.
Review — Dividing Multi-Digit Numbers: 468 ÷ 18 = ?
Answer 26
Why 26.
Review — Common Factors and Common Multiples: Greatest common factor of 16 and 40?
Answer 8
Why 8.
Warm Up
Straightforward practice. Get the method working first.
3 problemsGreatest common factor of 16 and 24?
Answer 8
Why 8.
Greatest common factor of 12 and 18?
Answer 6
Why Bigger than 3.
12 + 18 = 6 × (2 + ?). What is the missing number?
Answer 3
Why 18 ÷ 6.
Build It Up
The same ideas with more to keep track of.
2 problemsGreatest common factor of 15 and 25?
Answer 5
Why Both end in a 5 or 0.
15 + 25 = 5 × (3 + ?). What is the missing number?
Answer 5
Why 25 ÷ 5.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Common Factor: What is the greatest common factor of 20 and 30?
Answer 10
Why 10.
Inside the Bracket: 20 + 30 = 10 × (2 + ?). What goes in place of the question mark?
Answer 3
Why 10 × (2 + 3).