15 Mar 2013

Maths Help! Prime Numbers

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We've just learned factors, so today we went over Prime Numbers again. These are the numbers that only divide by 1 and themselves, e.g. 2 = 2 x 1, 3 = 3 x 1 and 5 = 5 x 1.

It's a great set of numbers to learn, as it helps kids with their mental maths and later on when doing Surds, equations and other tricky stuff. It's also a nice thing to practise as it lets them use their times tables to rule out which numbers can't be prime.

The rule we used is: no primes are even, except 2.

Then we worked through the entire number line working out which were prime, and which weren't. It's quick to do, and a great maths workout. The Amazing Maths Boy figured out the answers a lot quicker than I did:

2  3  5  7  11  13  17  19  23  29  31  37  41  43 etc

I was really impressed, and then the conversation turned like this:

Me: So what's the next prime number after 31?
Amazing Maths Boy: Is it 39?
Me: Don't 30 and 9 both divide by 3?
Amazing Maths Boy: Doh.