## Wednesday, 25 January 2012

### Prime Problem?

This morning our Year 6 class 'Magimixer' gave us 41 to make using the numbers 1,2,3,4 and 5.

(The idea is rather like the 2012 game - you use any of the 4 operations and must include all numbers in order to make the target.)

Normally we use our multiplication and factor knowledge to help us.  Straight away some of us saw that it was a prime number.  This generated such tries as (4 x 5 x 2) + 3 - 1 = 42 and others.
Try as we might, we couldn't make it unless we were a bit 'sneaky' and put numbers together e.g. 45 - 3 - 2 + 1

This left us asking the question, 'Is it impossible because it is prime?'
Maybe someone can tell us.
In the meantime we'll try some other primes with the same numbers...

1. (5 x 2 + 4) x 3 - 1 = 41

1. Thanks for this Michael. We obviously need to know our 14x table!

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3. Ha! One of my sixth formers spotted
(2+3+5) x 4 + 1
Obvious when she said it but I never saw that one!

1. Thank them, then! My class' reaction will be interesting...

4. Yesterday morning, we tried making other prime numbers with the same numbers and made each one we tried, easily!
The class were really impressed that sixth formers could solve our problem and we marvelled at the power of the internet!