Prime Numbers are like phone numbers - there is no real pattern to them and you can easily look them up. 

One of Einstein's colleagues asked him for his telephone number one day. Einstein reached for a telephone directory and looked it up. "You don't remember your own number?" the man asked, startled. "No," Einstein answered. "Why should I memorize something I can so easily get from a book?"

That said, to quickly complete some transfer test questions, you need to be able to recall the first few prime numbers quickly.

AQE advice on prime number questions

A prime number can only be divided evenly by itself and one.

Consider the whole number 5 - I have five sweets and want to share them out evenly - I can only give them all to one person or one each to five people. Five is, therefore, prime.


One is not a prime number

This is a source of much debate for mathematicians but let's just agree that it's not.

 

Two is the only even prime number.

The rest of the even numbers can be divided by two so they can't be prime.

 

No prime number greater than 5 ends in a 5.

Any number greater than 5 that ends in a 5 can be divided by 5.

 

Here are the first nineteen primes. Know these and I think that you'll be OK for the transfer test.

 

2

3

5

7

11

13

17

19

23

29

31

37

41

43

47

53

59

61

67

Notice that there is no 1? One is not, we may have mentioned, a prime number.


So how might this come up?

Sample transfer test question on prime numbers

 

When completing a question like this in the transfer test, encourage your child to cross through the non-primes by thinking of their times tables.

Remember that any multiple of three can quickly be tested by adding together the digits until you get down to a single digit - then if it's 3, 6 or 9 then the original number was a multiple of 3..

ie) 1234 → 1 + 2 + 3 + 4 = 10 → 1+0 = 1. Thus 1234 is not a multiple of 3.

but 1236 → 1 + 2 + 3 + 6 = 12 → 1+2 = 3. Thus 1236 is a multiple of 3.

 

 

[hint: the two prime numbers are 31 and 2. The answer is 62]



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