# Prime Numbers

Age Range: 7 - 11

Prime numbers are those numbers (greater than 1) that cannot be divided by any number except themselves and one.

The Greek Eratosthenes created a method to find out these prime numbers, although it only worked over a limited range:

1) Write out the numbers from 1 to 100 in ten rows of 10.

2) Cross off number 1, because all primes are greater than 1.

3) Number 2 is a prime, so we can keep it, but we need to cross off the multiples of 2 (i.e. even numbers).

4) Number 3 is also a prime, so again we keep it and cross off the multiples of 3.

5) The next number left is 5 (because four has been crossed off), so we keep it and cross of the multiples of this number.

6) The final number left in the first row is number 7, so cross off its multiples.

7) You have finished. All of the "surviving" numbers (coloured in white below) on your grid are prime numbers.

• Use the poster as a teaching resource or print it for use as a reference tool to share on children's tables.
• Add the prime numbers cards to your classroom displays or ask children to sort / order them.
• Use the banner and poster on your Maths classroom displays.

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### Dibo2000

i had a lot to learn today , thanks a lot .now this will help me with my maths lesson because my maths teacher is very strict

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### Jeff

me too, I had a extremely important mathematics test this afternoon and used this to work out and identify the Prime Numbers correctly 8)

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### Hi

oh thanks i have got my sats math tommorow and last week my maths teacher said prime numbers will be there and what is a prime number but thanks 2 u i now understand thanks

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### kiara2996

OMMGG!! this helps a lot!! ☺

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### kiara2996

i know me too my teacher always talk about tht and i never get it! but know i get it!! ☺

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### Danie26

wow thanks a lot!!! i have sats next week and i was really unsure on prime numbers and my teacher said ill probably get them in my paper so i searched them and this came up and now i really understand them but is there a quicker way of testing a number?

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### Mimi

I hardly understood what prime numbers are on another websits but this website taught me a lot i have got sats on thursday my maths one and now to this website i will be likely 2 pass it

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Great method for finding primes

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### Gabithomson95

i have my GCSE maths exam soon and i have never really understood the prime numbers but now thanks to this webiste.. i understand it better and i hope i can do well in my exam because of it

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### Smallperson22

This has really helped me learn my prime numbers for tuesday when i have my first GCSE maths exam!! :)

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### izzy

this is a really good way to lear about prime numbers  :)

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### Christinehill39

i knew nothing of prime numbers until i saw this. now i can help my daughter with her homework so thanks

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### Sony20

this is great thank you! ;)

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### rg

I'm doing my GCSE Maths, I find it hard and was confused to differentiate prime numbers, until i saw this... it explain really well... thank you very much

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### FatherOfSon

Thank you, i've show'd this to my child and he passed his SAT's thank you.

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### Rachel Gibson

i still don't get it got test tomorrow help!!! thanks anyway xx

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### Mrs. Anton

Thank you so much for this activity. It will save me a lot time to teach this concept.

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### Amy Taylor!

Really good way to learn prime numbers! I couldn't understand it before but now i do! thankyou!  x x x x

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### Mr.Pierce

Thanks for the help! You have no idea how much time this saved my class.s

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### Sheeskhan

Really good way to learn prime numbers! I couldn't understand it before but now i do! thank you!

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### Shees Khan Musakhail

Really good way to learn prime numbers! I couldn't understand it before but now i do! thank you!

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### Kavya

Thank you so much.The technique is very easy and can remember for a life time...It really helped a lot..

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### kacee

This is really helpful, THANK YOU so much

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### Noody Boobie

This has got me out of detention this website is the best!!!! I'm always going to use this website and tell my friends about it. :-)

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### Subrina

I now. Know what prime numbers are thanks to teaching ideas:)

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### Evan Bauer Tighe

I did this at home, and typed out all the primes and printed them. When it said in my SATS is this number a prime i was able to answer it! THNX

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### Indy

Thanks so much I'd already learnt this but i forgot how to do it so Thanks

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### Tilly

I had to do a huge project on anything to do with maths and this website has been a huge help!!!

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### hazy wazy

What a good site. My GCSE teacher is a diplomat's son and teaches at a good pace but sometimes I need to revise what he has taught to make it stick. I am so lucky to have a great teacher they are very scarce!

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### best paper writ...

This information is really helpful that it can give a pupil the technique on how to determine a prime number. It's really important and useful for them to know about this.

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### Alastair Carnegie

10,057 is the product of two prime numbers, but which ones? try this method:- 10,201 is the square of 101. and 10,201 - 10,057 = 144, and 144 = 12 x 12. so the two primes are 101 + 12, and 101 - 12, namely 113 x 89 = 10,057. ( this method does not always work, so try to figure out why?... and also how to correct it?)

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Thanks a lot

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### Jacob Ochen

Very fruitful resource, with great impact on kids mathematical concept.

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### Aiden

Useful to teach children prime numbers

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### Diana

Really nice! thank you for sharing :)

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### Michelle

THANK YOU for creating this colorful, helpful poster. I desperately need it for tutoring... :)

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### Tia

I really like this website

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perfect ideas

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This helps!

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super

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### Jenna

This website help me a lot for class today!Its a life saver.

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