how do you explain prime factors to a primary school child?

[workshy]

she gets it if it's obvious

eg 15=3x5

but if it's not made up of prime numbers she doesn't get it

any help?

A prime number is just a number that is not divisible by anything other than 1 and itself isn't it???

We make a factor tree, hard to show on here but
24 is made from say 2x12
2 is a prime factor, so that's the end of that branch
12 is made from say 2x6
2 is a prime factor so that's the end of that branch
6 is made from 2x3
both are prime so that's the end of all branches
so we have
2x2x2x3
which is
2 cubed x3
( It's much easier when you draw it!)

There's two books on Amazon called Mrs J Rocks' and 'Mrs J Rules` - I can't remember which is literacy and which is numeracy, but they explain things very simply.

PS it doesn't matter whether you start with 2x12 or 4x6 or 3x8, you will always end up with the same prime factors

thanks snowball3
I've seen the trees but she isn't usually very visual so didn't know if she would get them

I'll give it a go with her tomorrow :)