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prime numbers

I have a difficulty in trying to understand how to find out which numbers are prime. I don't understand how to work out if a number is prime when all it comes out as is a number which can be divided by 1 and itself. please don't think i'm being stupid or silly its just I have dyscalulia which makes maths more difficult to understand. could someone please explain it in a way I could understand?
thank you :smile:
It’s basically what u said a number is prime if it can ONLY be divided by one and itself example 31 is a prime number no other numbers can be multiplied to make it EXCEPT 1 and itself
So to find out if a number is a prime number see if 2 goes into it (if not) see if 3 does and so on
Hope that helped and didn’t confuse you more lol !! :smile:)
(edited 4 years ago)
Reply 2
Avatar for Rose22222
Rose22222
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4
Original post by 277263738
It’s basically what u said a number is prime if it can ONLY be divided by one and itself example 31 is a prime number no other numbers can be multiplied to make it EXCEPT 1 and itself
So to find out if a number is a prime number see if 2 goes into it (if not) see if 3 does and so on
Hope that helped and didn’t confuse you more lol !! :smile:)

so your saying I have to find out what makes the number if it is multiplied to be made? and if it is not it is a prime number???
Original post by Rose22222
so your saying I have to find out what makes the number if it is multiplied to be made? and if it is not it is a prime number???


If u can’t multiply any of those numbers in then yes it’s a prime number you don’t have to try and multiply all the numbers into it past the halfway value because you end up with a decimal to times it by ( trying to find out if 30 is a prime number don’t go past 15 because you will have to multiply those values by a decimal and that doesn’t count when trying to find prime numbers)
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Avatar for B_9710
B_9710
18
The question of whether a certain number is prime or not isn’t trivial. For small numbers it is easy. All you have to do is check that no positive whole number between 1 and the number itself divides the number. So for 7 as an example. The question is do any of 2,3,4,5,6 divide 7. The answer is no so it is prime.
Reply 5
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B_9710
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Original post by 277263738
If u can’t multiply any of those numbers in then yes it’s a prime number you don’t have to try and multiply all the numbers into it past the halfway value because you end up with a decimal to times it by ( trying to find out if 30 is a prime number don’t go past 15 because you will have to multiply those values by a decimal and that doesn’t count when trying to find prime numbers)

In fact you don’t have to check any factors greater than the square root of the number in question. So for 15 for example we only have to check numbers up to square root of 15. So only check numbers up to and including 3.
Reply 6
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Rose22222
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Original post by b_9710
in fact you don’t have to check any factors greater than the square root of the number in question. So for 15 for example we only have to check numbers up to square root of 15. So only check numbers up to and including 3.


Original post by 277263738
if u can’t multiply any of those numbers in then yes it’s a prime number you don’t have to try and multiply all the numbers into it past the halfway value because you end up with a decimal to times it by ( trying to find out if 30 is a prime number don’t go past 15 because you will have to multiply those values by a decimal and that doesn’t count when trying to find prime numbers)

thank you everyone!! I now understand :smile:

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