Unit 2 Section 1 : Factors and Prime Numbers
A factor is a whole number which divides exactly into a whole number, leaving no remainder.
For example, 13 is a factor of 52 because 13 divides exactly into 52 (52 ÷ 13 = 4 leaving no remainder).
The complete list of factors of 52 is: 1, 2, 4, 13, 26, and 52 (all these divide exactly into 52).
A prime number has exactly two factors, 1 and itself.
For example, 13 is a prime number because the only factors of 13 are 1 and 13.
The number 8 is not prime because it has four factors: 1, 2, 4 and 8.
The number 1 is not a prime number because it only has one factor (itself).
Practice Question 1
You are going to work out which of the whole numbers from 1 to 10 are prime.
You will start by working out the factors of each number  the prime numbers are the ones with exactly two factors.
Work out the factors of each number then click on the button marked
to see whether you are correct.
The factors of 1 are 

The factors of 2 are 

The factors of 3 are 

The factors of 4 are 

The factors of 5 are 

The factors of 6 are 

The factors of 7 are 

The factors of 8 are 

The factors of 9 are 

The factors of 10 are 

Which of the numbers 1 to 10 are prime numbers?
Practice Question 2
Work out which of the following numbers are prime numbers : 18, 45, 79, 90 and 97.
Is the number 18 prime? 

Is the number 45 prime? 

Is the number 79 prime? 

Is the number 90 prime? 

Is the number 97 prime? 

Practice Question 3
Work out the prime factors of the number 24.
To do this you need to find all the factors of 24, then check which ones are prime.
(a) What are the factors of 24?
(b) What are the prime factors of 24?
Exercises
Work out the answers to the questions below and fill in the boxes. Click on the
button to find out whether you have answered correctly. If you are right
then will appear and you should move on to the next
question. If appears then your answer is wrong. Click
on to clear your original answer and have another go.
If you can't work out the right answer then click on
to see
the answer.
In this section you need to give a list of numbers for some of the answers.
The order doesn't matter, but separate the numbers with commas, like this:
You have now completed Unit 2 Section 1
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