HCF

What is HCF ?

Let's see what it means ....

Note: 1 is not a prime number so you do not have to use it for prime factorization.

It doesn't matter which two factors

you start with you will always end up

with the same prime factors.

2X2X2X2X3

Using Prime factors

We cn use the prime factors of a number to help us see other relationships.

Eg. Prime factors of 30

As 2, 3 and 5 are prime factors of 30. We can use this to find the other factors of 30.

30= 2X3X5 = 6X5 . So, 6 is also a factor of 30.

30= 2X3X5 = 2X15 . So, 15 also is a factor of 15

30= 2X5X3=10X3. So, 10 is also a factor of 30.

Open Ended

Four common factors of 80 and 100

Open Ended

Four examples of Co-prime numbers

Open Ended

Four examples of twin - prime numbers

Multiple Select

The numbers divisible by 4

• 21324

• 49514

• 391751

• 397016

• 531608

Multiple Choice

If the sum of the digits is divisible by 9 then the number must be divisible by

• 9

• 6

• 3

• 3 and 9

Multiple Select

Numbers divisible by 3

• 235671

• 970384

• 28191

• 20200

• 29607

Multiple Choice

A number divisible by 9 is also divisible by 3.

• true

• false

Multiple Choice

Numbers divisible by 3 are also divisible by 6

• true

• false

Multiple Choice

Numbers divisible by 6 are also divisible by 3

• true

• false

Open Ended

Use the prime factors to find the HCF (14,24) :

Multiple Choice

HCF (14, 28) is

• 1

• 14

• 28

• none

Multiple Choice

There is only one common factor of 6 and 12.

• true

• false

Multiple Choice

The greatest factor of a number is

• 1

• 0

• 2

• the number itself

Multiple Choice

All even numbers are divisible by

• 10

• 5

• 2

• all of above

Multiple Choice

The greatest factor of a number is

• 1

• 0

• 2

• the number itself