Active discussions

Meet the Other Phone. Only the apps you allow.

Meet the Other Phone.
Only the apps you allow.

Buy now

Please or to access all these features

Talk
Education

Join the discussion on our Education forum.

Original poster

Very tricky maths problem for 10 year old?

82 replies

robinia · 11/07/2006 22:51

Dd, along with selected others of her class, has been given a maths problem which I can't work out and nor can dh:

Using numbers 2, 4, 6 and 8 and "divided by" and "equals", make every number from 1 to 32.
eg. 1 = 8 divided by 8; Can't use plus, minus or multiply. Can use each of the numbers as many times as necessary.

We can only get about 1/4 of the answers. Can anybody enlighten us and isn't this a bit tough for a 10year old or is this the way they teach maths these days?

OP posts:
NotQuiteCockney · 13/07/2006 19:39

Look. It cannot be done. And this is why.

Dividing and multiplying are basically the same operation, right?

And when you multiply things together, you can't get primes you didn't start out with, because, duh, that's the definition of a prime.

Not possible. End of.

I am 100% sure this is a misunderstanding somewhere. Maybe they were meant to try to get as many as they could with just /, and then try other operators for the rest?

Piffle · 13/07/2006 20:02

it must be as you can divide and get fractions
4/.8 = 5
you get .8 by dividing 8/10
Not that I've got the 10 you understand
Preg brain here too well thats my excuse

foxinsocks · 13/07/2006 20:05

I imagine they were meant to get as many as they could and then learn the lesson that you can't get the primes (perhaps) and factors thereof.

NotQuiteCockney · 13/07/2006 20:09

Piffle, to get .8, you need 4/5. Which requires you to have 5.

You really can't get 5 unless you start out with 5.

dixia · 13/07/2006 20:11

Hmmm...

I agree with notquitecockney. Now I am multiplying correctly I am sure it cant be done. Also think there was a mix up when copying down homework.

Piffle, if you had the 10, you would have a multiple of the prime number in question, therefore being able to get it as an answer using division.

If you can't make a multiple of a specific prime number using the digits provided, then you can't get back to the original prime.

I await results from mum and sis, but dont' think they will be able to do it either.

Piffle · 13/07/2006 20:45

8/10 is the same but give you the option of using an even number to divide by, therefore not needing the 5.
But like I said I cannot get the 10 so I'm talking horses botties really

dixia · 13/07/2006 20:47

My brain hurts

NotQuiteCockney · 13/07/2006 20:48

Yes, but to get the 10, you need a 5. The problem isn't getting even numbers, it's getting odd numbers, iyswim.

Original poster
robinia · 13/07/2006 23:12

Sorry to be bugging so many. I'll be seeing the teacher on Tuesday if you can all bear to wait that long. I totally agree with you nqc about the primes - I spent a long time trying to make some numbers which had lots of factors (so long since I did maths that I've forgotten if that's the correct word). eg. 72 has factors 2,3,4,6,8,9,12etc. and work backwards but as you say numbers which have factor 5 can't be made with the numbers we've got.

And dd (and friend)'s words were - "division only - if we get stuck we can use the others (x,+,-) but Mrs. H. says they can all be done with division".

OP posts:
yajorome · 13/07/2006 23:15

I would think it's a 'look what primes are' type problem, ie a learning experience? Go from 1-32, break them down into primes, those not in the set of primes you're given (1, 2, 3) you can't do, because that's what makes primes, well, prime. Right?

yajorome · 13/07/2006 23:17

Oops - crossposted. Will be curious to see what her answers are! (Must add thread to watch list... )

yajorome · 15/07/2006 01:21

and....

Am quite curious about this. Reallly do hope it's not clever and is a maths problem. Rob - please do let us know! Fab of your dd.

lemonaid · 03/08/2006 16:19

So what was the teacher's verdict?

merrily · 03/08/2006 16:42

I've just read through this thread and now want to know how it's done! please do tell!

Tinker · 03/08/2006 16:50

Which ones can't you make?

Tinker · 03/08/2006 16:50

Ignore me, am late to this thread

prettybird · 03/08/2006 17:21

if you can use the numbers as many times as necessary, can yuo not just use (2/4)+(2/4)+(2/4)+(2/4) (10 times) to get 5? ie 10 x 0.5 = 5

And ditto for the other numbers that are a problem? ie do 2/4 + 2/4 (14 times) tp get 7?

Or am I missing something?

beckybrastraps · 03/08/2006 17:23

You can't add.

foxinsocks · 03/08/2006 17:23

can't use plus

prettybird · 03/08/2006 17:29

I did ask if I was missing something!

aDAdOnMumsnet · 03/08/2006 17:40

Sorry v late to this thread - probably just as well as this would have bugged me for days rather than just a few minutes!

I agree with anyone saying the prime numbers MUST be impossible no?? That's how it seems to my not very mathematical brain.

Am I right in saying that this wasn't resolved by teacher before the school holidays, and we have to wait for weeks for an answer?!

I wish I had never seen this thread.

WriggleJiggle · 03/08/2006 23:10

What an exciting challenge to keep me occupied during those long drawn out bf sessions.
Thanks!

Salamander · 04/08/2006 10:23

Where's Vorderman when you need her?

Quootiepie · 04/08/2006 10:26

cant you use square roots and things?

Quootiepie · 04/08/2006 10:26

or powers?

Swipe left for the next trending thread