Cogito
Grade 6 Math · Chapter 3 · Lesson 3
Common Factors and Common Multiples
What two numbers share.
10 problems · about 17 minutes · 6.NS.B.4
What this lesson teaches
The child finds the greatest common factor and least common multiple of two numbers and uses the distributive property.
- A common factor divides both numbers.
- A common multiple is divided by both.
- The greatest common factor can be taken outside a sum.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Multiplying and Dividing Decimals: 9 ÷ 0.3 = ?
Answer 30
Why 30.
Review — Dividing a Fraction by a Fraction: 3/4 ÷ 1/12 = ?
Answer 9
Why 9.
Warm Up
Straightforward practice. Get the method working first.
4 problemsGreatest common factor of 16 and 40?
Answer 8
Why 8.
Which is never bigger than the smaller number?
Answer A common factor.
Why A common factor is at most the smaller number.
Greatest common factor of 18 and 24?
Answer 6
Why 1, 2, 3, 6 divide both.
Least common multiple of 4 and 10?
Answer 20
Why 4, 8, 12, 16, 20.
Build It Up
The same ideas with more to keep track of.
2 problemsGreatest common factor of 15 and 25?
Answer 5
Why Both are multiples of 5.
14 + 21 = 7(2 + ?). What is the missing number?
Answer 3
Why 21 ÷ 7.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Bags: 24 apples and 36 pears into identical bags. What is the greatest number of bags?
Answer 12 bags
Why 12 bags.
The Buses: One bus every 6 minutes, another every 8. After how many minutes do both come together?
Answer 24 minutes
Why 24 minutes.