# Year 5

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### We can work out which numbers less than 100 are prime numbers

##### Year 5 Unit 17

#### What we are learning:

- Prime numbers are numbers that can
**only**be divided by 1 and themselves without a remainder. - The first prime number is therefore the number 1 itself.
- The next one is 2 because it can only be divided (without a remainder) by 1 and 2.
- The next one is 3 because it can only be divided by 1 and 3.
- The next ones are 5, 7, 11, 13, 17, 19……
- Apart from the number 2, all prime numbers are odd, but not all odd numbers are prime!

##### ACTIVITY 1: EXPLORING PRIME NUMBERS

#### Activities you can do at home:

Explore all the prime numbers you can find together up to 100. Be careful to check that they are prime, and that nothing else will divide into them other than 1 and the number itself.

You need to know your tables to work out which numbers are prime!

#### Good questions to ask:

Can you explain what a prime number is?

Is 5 a prime number? How do you know?

Can 15 be a prime number? Why not?

#### If your child:

Cannot identify which numbers are prime

Take a low prime number, e.g. 13 and explore which other number will go into it without leaving a remainder. The answer will be 1 and 13. Now try 12, where you will find that 1, 2, 3, 4, 6 and 12 all go into it without leaving a remainder

Knows or can work out all the prime numbers to 100

Look for prime numbers over 100 together. How does your child set about finding them?

##### Extension Activity

Please use this activity when you think your child understands the unit of work. It will deepen and extend your child’s understanding of this unit.