Saxon Lesson 25

Saxon Lesson 25

Factors of a Whole Number

Learning Goal

I can list all the factors of a whole number

Poll

I can list all the factors of a whole number

• I can't remember what a factor is,

  let alone give you a list of them!

• I know what a factor is.

• I can do this,

  I just don't list them correctly

• I got this!

  I can list them IN the correct order.

Multiple Choice

Let's test our vocab skills!

Select the word that best matches the following description:

"the result of division"

• Remainder

• Divisor

• Quotient

• Divisible

Multiple Choice

Select the word that best matches the following description:

"all the numbers in this sequence: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9..."

• Prime Number

• Whole number

• Factor

• Remainder

Multiple Choice

Select the word that best matches the following description:

"An amount left after division"

• Remainder

• Quotient

• Divisor

• Divisible

List the factors of 20

One way we can do this is to start with 1 and divide 20 without leaving a remainder.  

20 ÷  1 = 20

20 ÷  2 = 10

20 ÷  4 = 5

             

* You can reduce your search for factors if you record the quotient when finding a factor. 1,  2, 4, 5, 10, 20

Divisibility rules

Sometimes we can discover some factors of a number just by looking at one or two of its digits.

For example:

all even whole numbers has 2 as a factor.

a whole number that ends in 0 or 5 has 5 as a factor.

a whole number that ends in 0 has 10, 5, and 2 as a factor

Since 20 is an even number and ends in a 0, we know that 2, 5, and 10 were factors of 20.

List the factors of 20

Another way we can do this is to start with 1 and multiply to get to the product of 20.   

1 x 20 = 20

2 x 10 = 20 

4 x 5 = 20 

             

1,  2, 4, 5, 10, 20

Prime numbers

Every number greater than 1 has at least two factors: the number 1 and itself.

Counting numbers that only has two factors - 1 and itself - is called a prime number.

Multiple Choice

Which of these numbers is not a factor of 30?

• 2

• 3

• 4

• 5

Multiple Choice

Which factor of 9 is also a factor of 18?

• 2

• 3

• 4

• 5

Composite numbers

Counting numbers that only has more than two factors is called a composite number.

Example: Factors of 15 are: 1, 3, 5, 15

1 x 15 = 15

3 x 5 = 15

Multiple Choice

Let's test our mad math skills!

Select the word that best matches the following description:

"a counting number greater than 1 whose only two factors are the number 1 and itself"

• Prime Number

• Whole Number

• Factor

• Composite Number

Multiple Choice

Select the word that best matches the following description:

"any of the numbers multiplied in a multiplication problem" and

"are all the whole numbers that can divide without leaving a remainder"?

• Prime Number

• Whole Number

• Factor

• Remainder

Multiple Choice

Select the word that best matches the following description:

"capable of being divided without a remainder"

• quotient

• divisible

• dividend

• factor

Multiple Choice

Select the picture that best matches the following description:

"Who lives in the ocean, under the sea"?

Multiple Choice

The number 19 is an example of a ________ number.

• prime

• composite

Multiple Choice

Select the picture that best matches the best way to remember what a prime number is: