1. Whole Numbers
Factors
What will we learn today?
• determining if a 1-digit number is a
factor of a given number,
• listing all factors of a given
number up to 100,
• finding the common factors
of two given numbers

2. What are factors?
A factor is a smaller number that
divides exactly any larger number and
gives the remainder zero.
For example,
6 is not "exactly divisible" by 4 and 5.
So, 4 and 5 are not factors of 6.

3. How to find factors of a number?
We will find all the factors of 12 by finding all
the numbers that 12 can be exactly divided by.
12 ÷ 1 = 12 12 ÷ 2 = 6 12 ÷ 3 = 4
12 ÷ 4 = 3 12 ÷ 6 = 2 12 ÷ 12 = 1
12 is exactly divisible by 1, 2, 3, 4, 6 and 12.
So 1, 2, 3, 4, 6 and 12 are the factors of 12.

4. Write all the factors for the numbers below
(the first one is done for you):
4 1 2 4
7 1 7
9 1 3
15 1 15

5. Write all the factors for the numbers below
(the first one is done for you):
4 1 2 4
7 1 7 1x7=7
9 1 3
15 1 15

6. Write all the factors for the numbers below
(the first one is done for you):
4 1 2 4
7 1 7 1x7=7
9 1 3 9 1x9=9,3x3=9
15 1 15

7. Write all the factors for the numbers below
(the first one is done for you):
4 1 2 4
7 1 7 1x7=7
9 1 3 9 1x9=9,3x3=9
15 1 3 5 15 1 x 15 = 15
3 x 5 = 15

8. What are the factors of 20?

9. What are the factors of 20?
1 x 20 = 20
2 x 10 = 20
4 x 5 = 20
Step 1:
Write down the multiplication sentences of 20.

10. What are the factors of 20?
1 x 20 = 20
2 x 10 = 20
4 x 5 = 20
Step 2:
Do not write the factors twice.
4 x 5 = 5 x 4.
You only need to write down 4 and 5 once.

11. What are the factors of 20?
1 x 20 = 20
2 x 10 = 20
4 x 5 = 20
20 is exactly divisible by 1, 2, 4, 5, 10 and 20.
So 1, 2, 4, 5, 10 and 20 are the factors of 20.

12. What are the common factors
of 40 and 72?

13. What are the common factors
of 40 and 72?
1 x 40 = 40 1 x 72 = 72
2 x 20 = 40 2 x 36 = 72
4 x 10 = 40 3 x 24 = 72
4 x 18 = 72
5 x 8 = 40
6 x 12 = 72
8 x 9 = 72
Step 1:
List down all the factors.

14. What are the common factors
of 40 and 72?
1 x 40 = 40 1 x 72 = 72
2 x 20 = 40 2 x 36 = 72
4 x 10 = 40 3 x 24 = 72
4 x 18 = 72
5 x 8 = 40
6 x 12 = 72
8 x 9 = 72
Step 2:
Circle the common number you see.

15. What are the common factors
of 40 and 72?
1 x 40 = 40 1 x 72 = 72
2 x 20 = 40 2 x 36 = 72
4 x 10 = 40 3 x 24 = 72
4 x 18 = 72
5 x 8 = 40
6 x 12 = 72
8 x 9 = 72
The common factors are 1, 2, 4 and 8.

16. Are you ready to
try out the
questions?