prime and factors
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prime and factors
hi,
My son is preparing for the 11+ exam in Essex.
I'd like to know if anyone know a easy method to learn prime numbers and factors
for agiven numbers
thnx
My son is preparing for the 11+ exam in Essex.
I'd like to know if anyone know a easy method to learn prime numbers and factors
for agiven numbers
thnx
Hi P&A
Assuming you are looking to write a number as a product of its primes.
A prime number has two distinct factors, itself and 1.
2 is the only even prime number, becasue it only has two factors, 2 and 1.
Any number can be written as a product of its primes.
First identify the prime numbers using eratosthenes sieve.
http://www.teachingideas.co.uk/maths/prime.htm
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71
are the first twenty prime numbers.
Now choose at random any number, say 48
Start by dividing by 2
48 divided by 2 equal 24
24 divided by 2 equals 12
12 divided by 2 equals 6
6 divided by 2 equals 3
3 is a prime number so you cannot continue
48 can be written as 2 x 2 x 2 x 2 x 3, the product of its primes.
Try again with 63
63 is an odd number so cannot be divided by 2, so try 3
63 divided by 3 is 21
21 divided by 3 is 7
7 is a prime number so you cannot continue
63 can be written as 3 x 3 x 7, the product of its primes
Try again with 35
Can´t divide by 2, Can´t divide by 3, try 5
35 divided by 5 equals 7
7 is a prime number so you cannot continue
35 can be written as 5 x 7
Try 71
Can´t divide by any prime number except itself.
So 71, must be a prime number.
Keep practicing.
The product of primes is used to identify highest common factors and lowest common multiples of different numbers.
Hope this helps
Regards
Mike
Assuming you are looking to write a number as a product of its primes.
A prime number has two distinct factors, itself and 1.
2 is the only even prime number, becasue it only has two factors, 2 and 1.
Any number can be written as a product of its primes.
First identify the prime numbers using eratosthenes sieve.
http://www.teachingideas.co.uk/maths/prime.htm
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71
are the first twenty prime numbers.
Now choose at random any number, say 48
Start by dividing by 2
48 divided by 2 equal 24
24 divided by 2 equals 12
12 divided by 2 equals 6
6 divided by 2 equals 3
3 is a prime number so you cannot continue
48 can be written as 2 x 2 x 2 x 2 x 3, the product of its primes.
Try again with 63
63 is an odd number so cannot be divided by 2, so try 3
63 divided by 3 is 21
21 divided by 3 is 7
7 is a prime number so you cannot continue
63 can be written as 3 x 3 x 7, the product of its primes
Try again with 35
Can´t divide by 2, Can´t divide by 3, try 5
35 divided by 5 equals 7
7 is a prime number so you cannot continue
35 can be written as 5 x 7
Try 71
Can´t divide by any prime number except itself.
So 71, must be a prime number.
Keep practicing.
The product of primes is used to identify highest common factors and lowest common multiples of different numbers.
Hope this helps
Regards
Mike
oops Mike.
Hi Mike,
I was just looking at your demonstration of prime numbers and I noticed a small error.
63/3 does not equal 31. This is 21 which can then be divided again by three and this gives you 7 which is the the prime number.
Thanks
Jams Year5
I was just looking at your demonstration of prime numbers and I noticed a small error.
63/3 does not equal 31. This is 21 which can then be divided again by three and this gives you 7 which is the the prime number.
Thanks
Jams Year5