Math Intervention 3–5 Grade

Multifaceted Number Concepts 215

Finding Common Factors

CONCEPT:

What is the Finding Common Factors Concept?

A factor of a number will divide that number evenly. For

example, 9 is a factor of 18 because 18 can be divided by

9 without any remainders or fractional parts of a number.

Eighteen has other factors, too. It is also divided evenly by

6 and 3, also by 1 and itself. The factors of 18 are 1, 2, 3, 6, 9,

18. If a number is only divisible by 1 and itself, it is a prime
    number. Often the task is to fi nd common factors of two or
    more numbers. For example, 5 is a common factor of 30 and
    20 because 5 is a factor of 30 and of 20. In fact, 1, 2, 5, 10 are
    all common factors of 30 and 20. If the task is to fi nd the
    greatest common factor (GCF) of 30 and 20, we compare the
    factors of 30 and the factors of 20 to fi nd the largest common
    factor, which is 10.

CCSS

Operations and Algebraic Thinking

Formative Assessment

To fi nd out if a student understands the fi nding factors

concept ask the student to name at least fi ve factors of the

following numbers:

12 50 48

Then ask the student to fi nd at least two common factors of

the following pairs of numbers:

15, 35 12, 18 36, 16

Then ask the student to fi nd the GCF of the following numbers:

9, 12, 24 18, 48, 30 33, 7, 2 0