# Talk

## What is the 9th multiple of 2?

(31 Posts)
Erebus Tue 13-Sep-11 15:57:18

or the 3rd multiple of 2?

Do they mean 9 x 2 (= 18!) and
3 x 2 (= 6 of course)

OR does the first mean 2x2x2x2x2x2x2 etc 9 times and the other
2x2x2? etc.

Tue 13-Sep-11 16:02:25

At first thought i would have said 18.

But reading your post has confuddled the hell out of me, so in all honesty i haven't a friggin clue!

Tue 13-Sep-11 16:05:33

I would say that means 2 to the exponent 9 (ie, 2x2x2x2x2x2x2x2x2).

Tue 13-Sep-11 16:08:33

2x2x2x2x2x2x2x2x2 would be expressed as 'the ninth power of 2' I think.

FagButt Tue 13-Sep-11 16:09:04

512 ??

GrimmaTheNome Tue 13-Sep-11 16:09:29

What's the context of this question? I can't remember ever having heard either straightforward multiplication or exponentiation expressed this way.

FagButt Tue 13-Sep-11 16:10:30

2x2 = 4
x2= 8
x2 = 16
x2 = 32 etc

til you have multiplied it 9 times = 512 i think

Tue 13-Sep-11 16:10:36

Yes, see here

'The ninth multiple of 2' is just a fancy way of saying '2x9'

Tue 13-Sep-11 16:10:54

It's definitely 18

FagButt Tue 13-Sep-11 16:13:03

oh

so would 9 to the power of 2 be 512 ?

never got my maths o level !

StuckUpTheFarawayTree Tue 13-Sep-11 16:13:36

I agree. 18. Just 9x2

Erebus Tue 13-Sep-11 16:25:38

Thanks all!

DS was 'pleased' to see it confuddled us grown ups too!

Tue 13-Sep-11 16:43:23

Yes, 2^9=512

Floggingmolly Tue 13-Sep-11 17:05:30

Can't see the link Lougle, but you're totally correct

AnyoneButLulu Tue 13-Sep-11 17:13:28

Fagbutt, no, 9 to the power of 2 (aka 9 squared) = 81.
2 to the power of 9 = 512

9th multiple of 2 is a new one on me, and my degree is in maths. I do think primary maths teachers just make phrases up to confuse us sometimes.

FagButt Tue 13-Sep-11 17:34:14

thanks anyone, i shall withdraw from all mathematical threads

spanieleyes Tue 13-Sep-11 17:54:42

The teacher isn't being deliberately confusing, honest! Children learn what multiples are, so the multiples of 4 are 8,16,24,32,40 etc. They also learn to identify if a number is a multiple of another, so will be asked, say, is 81 a multiple of 9, is 762 a multiple of 3 and will learn the rules which tell them how to work these out. Multiples ( and factors) are linked together and children need to know the vocabulary associated with them. SO children do need to work out the nth multiple of a given number ( even if initially this just means multiply the two numbers together!)

Tue 13-Sep-11 18:32:23

Anyonebutlulu

The concept of multiples has not been made up by the teacher, as spanieleyes has said, the multiples of 2 are 2, 4, 6, 8, etc so the 9th multiple of 2 is 18

JellyBelly10 Tue 13-Sep-11 18:34:10

Oh my god, when my DS gets further up the school and starts asking these sort of questions I'm going to look like a total twonk as won't have a clue! Luckily he's currently just gone into Y2 and other DS is in YR so hopefully it'll be a while before this level of question?!

GrimmaTheNome Tue 13-Sep-11 18:40:30

>The concept of multiples has not been made up by the teacher

no, but it is a superfluous piece of terminology - most of us have learned to multiply numbers without it.

The other term which was new to me was 'number bonds' though that term perhaps has a little more usefulness. I realised what it meant, but it did occur to me that perhaps primary schools should issue parents with a glossary of newfangled terms - and an explanation of what computational methods they prefer at each stage so we don't confuse our kids by teaching them long division the way we were taught etc

Tue 13-Sep-11 18:45:47

well i would have said 18 also.

dd has just started yr 5 and to be perfectly honest, i feel like a complete tool when i have no idea what she's talking about. The terminology in maths has changed, the methods are long winded (and yes i understand the thinking behind this) but oh my god, i was crap at 'getting it' the first time round.

spanieleyes Tue 13-Sep-11 18:59:21

Sorry, but it's not "superfluous". You are not learning to multiply, you are learning to find multiples. For example, 3,4.5,6,7.5 are multiples but wouldn't be in any times tables you would learn ( unless you like learning your 1 and a half times tables!) Multiples are used in a wide range of maths, you need to find common multiples of numbers, these are incredibly important when dealing with fractions. It may not have been a common term in primary schools when we were young, but it is now!

pointydog Tue 13-Sep-11 19:12:02

18

pointydog Tue 13-Sep-11 19:12:48

Is it new-fangled? I wouldn't have thought so. You need to talk about multiples in maths from time to time.

susiedaisy Tue 13-Sep-11 19:12:50

20

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