## Unit 2 Section 1 : Factors and Prime Numbers

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** 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 Click
on this button below to see the correct answer 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

Source: www.cimt.plymouth.ac.uk/projects/mepres/book8/bk8i2/bk8_2i1.htm