# Talk

## Year 8 ALGEBRA hellllllpppp! OMG I can't believe they expect 12 year olds to do this.

(32 Posts)
Mon 17-Oct-11 17:18:44

My daughter's in tears about her homework.

There are three sections marked MUST (be able to do), SHOULD and COULD.

We're half way through MUST and stuck and it's not for want of extensive googling.

I'd be really grateful if anyone could tell me what the answer is and how you worked it out.

Half (as in the fraction one over two) to the power of minus 3.

But that isn't algebra? Are they asking her to calculate it? If so I presume that she is allowed to use a calculator?

FroOOOOOtshoOOOOOOts Mon 17-Oct-11 17:26:47

ok the answer is 8 (apparently)
but it's really hard to explain
[http://uk.answers.yahoo.com/question/index?qid=20100827020014AAHKqsN this]] explains it using half to the power -2
HTH

FroOOOOOtshoOOOOOOts Mon 17-Oct-11 17:27:05
simonthedog Mon 17-Oct-11 17:27:17

Its half x half x half and minus x minus x minus which works out as minus one eighth i think!

schobe Mon 17-Oct-11 17:27:18

It means the inverse of a half, then raise to the power of 3. So flip 1/2 upside down (inverse) and it becomes 2/1 which is just 2. Then do 2 to the power of 3, ie 2 cubed.

Not used very rigorous language there, but hope it makes sense.

schobe Mon 17-Oct-11 17:28:23

yy, not algebra. I guess a precursor to algebra if anything.

simonthedog Mon 17-Oct-11 17:31:22

No sorry the above posters are right it's 8 (oh dear and I got a B in my further maths a level - was a long time ago )

Ben10WasTheSpawnNowWeLoveLego Mon 17-Oct-11 17:31:27

I have no idea what any of you are going on about... and they expect a year 8 to do this?! I have no chance of ever helping DS with his secondary school maths homework

noblegiraffe Mon 17-Oct-11 17:43:37

This is grade A GCSE stuff, so beyond level 8 and therefore ridiculous to have as a 'All MUST' objective, especially for the start of Y8.

The mind boggles as to what the harder stuff will be.

I would send in a note saying that it was too difficult. Don't waste your time on it any further, it is not worth crying over.

iggly2 Mon 17-Oct-11 17:56:46

If a number is to a negative power than first find the recipricol eg 1/2 becomes 2/1=2 then do that number to the original power so........ 2 power3=8.
HTH

RitaMorgan Mon 17-Oct-11 17:59:21

Didn't she do this in class?

If she doesn't understand it, she should go and see the teacher tomorrow. Googling the answers and getting your mum to help isn't doing her any good - the point of homework is to check that she has understood the class work. You're doing her no favours.

Mon 17-Oct-11 18:06:42

DS1 is in Y* and able at maths.

He had a quick look and said "probably something like -1.5. He only ever has a quick look at anything, so if he couldn't do it then I wouldn't expect any other Y8 to do it unless they were exceptional.

MindtheGappp Mon 17-Oct-11 18:21:01

"One over two to the minus three" is the same as "two to the three" or "two cubed".

Answer = 8, as others have said.

My DD is in Y8 - I will ask her if she has done this work.

Mon 17-Oct-11 19:55:34

Thanks all. We got there in the end. It is indeed 8. In the COULD section there are things like 625 over 16 in brackets to the power of minus 3/4. Insanely hard. I'm glad some of you think so too.

Rita I disagree that it's not doing her any good and there's no point expecting her to go into class and sort it out because she has an utterly shite maths teacher for the second year running. Because of this we are having to work at home to have any chance at understanding what she is supposed to be learning there.

Her classmates are struggling too and they can afford maths tutors luckily for them. We can't so it'll just have to be me.

Thanks for you help everyone. I may be back. [flowers]

Mon 17-Oct-11 20:02:27

By the way it was I, not the school, who thought it was algebra. Which just goes to show what a long way I have come this evening.

noblegiraffe Mon 17-Oct-11 20:14:37

What level is your DD working at (what did she get at the end of Y7) and what is her KS3 target?

Because that MUST section is wildly inappropriate as an expectation for a whole Y8 class (even a top set) and the COULD section would fox all but the brightest GCSE candidate. (If you want evidence, look here and click on the Powers and Surds document under 'Grade A' - question 3c is A* and still easier than the one you described in the COULD section)

I would contact the school and ask why she is being set this level of work and if it is in line with the Y8 Scheme of Work. Your DD is potentially being put off maths by either ludicrously high expectations, or a teacher who doesn't know what they're doing.

GrimmaTheNome Mon 17-Oct-11 20:17:03

This is one of those things that's fairly straightforward if you know what 'to the power of -3' means and impossible otherwise. After typing that, I showed it to my yr8 DD (at a grammar school and good at maths) - asked her if she'd come across that (no), explained it to her and she said pretty much what I did. If it hadn't been properly explained in class, no way.

I think I got off lightly tonight with DD raging at interior and exterior angles - which she could do once she'd been arsed to look at her textbook to remind herself what to do as an alternative to me confusing her by working it out from first principles. Things like 'if the exterior angle of a polygon is 4 degrees how many sides has it got'

DeWe Mon 17-Oct-11 20:19:24

Assuming it was taught properly it isn't really hard. But if you haven't been shown properly it would be pretty nigh impossible to guess/know intuitively.

It wasn't meant as a calculator exercise was it? Then it would be fairly easy.

Basically negative powers invert the number ie(x/ y)^-z = (y/x)^z

Fraction powers are more interesting as it equates to the root. So x^(1/2)= square root of x. and y^(1/3)= cube root of y

If you're interested and can understand what I write... it's much harder to explain in writing to me...

(625/16)^-(3/4)
Invert and get rid of the minus sign first: =(16/625)^3/4

You can look at ^3/4 in two stages.
Look at ^ 1/4 first. That means fourth root: (ie if n x n x n x n = N then fourth root of N =n)
So look at (16/625)^1/4
2 x 2 x 2 x 2 =16 so fourth root of 16 is 2
5 x 5 x 5 x 5 =625 so fourth root of 625 is 5

So (16/625)^1/4 = 2/5

Now you need to put that to the power 3.
2^3 = 2 x 2 x 2 =8
5^3 = 5 x 5 x 5 = 125

So (2/5)^ 3 = 8/125

Answer: (625/16) ^ -(3/4) = 8/125

None of the steps are difficult, but if you don't know what it means you're sunk really. If you think the teacher will handle it well then it might be worth writing in her book that she seems to have got a bit confused, could he go through it properly.

I'd suggest you show her how to do it on the calculator. There should be a button on which (probably) you have X^y
If you want to do say (1/2)^ -3 then press:
[1/2] [button X^y] [minus 3] then [equals] should give you the answer.

GrimmaTheNome Mon 17-Oct-11 21:10:37

I just checked DDs yr8 national curriculum textbook. Negative powers are there in the first chapter (evidently her teacher isn't just going through it from start to finish) so - provided it was adequately explained - the 'must' question is yr8- appropriate. I couldn't see anything at all about fractional powers - in fact, there seemed to be various mentions of square roots but I couldn't see anything about cube roots or higher roots. Which suggests the 'could' question is out of line with national curriculum for this age.

Mon 17-Oct-11 21:23:43

I'm glad you COULD stuff is too hard. Thanks for the link NobleGiraffe. It has made my dd feel a bit better. I think I will be going into school to have a chat after half term.

Dewe thanks for the explanation. I had to look up what^ means. I guess it's just a case of learning it then practising it so it somehow sticks.

DD is still doing homework. She's doing over 4 hours every day! It's absolutely crazy. She's so stressed and taking it out on everyone else. It also means I don't dare ask her to do the stuff she's meant to do to earn pocket money. I'm really begining to resent the impact this amount of homework is having on family life. I guess that's a whole other thread.

Thanks again for your help and support on this.

LoveInAColdGrave Mon 17-Oct-11 21:30:11

Oh dear god. Am pregnant with DC1 and this thread has given me another thing to worry about. There is no way I could help with this .

IloveJudgeJudy Mon 17-Oct-11 23:08:18

Your DD is doing 4 hours HW a night? That's far too much. We've just had a talk about Y8 at school (DS2) and if they're doing more than 1 1/2 to 2 hours per night that's far too much. They've told us to go back to school and tell the SLT if that's the case as that is the school's fault. Your DD can't go on like this. She'll crack up.

Mon 17-Oct-11 23:10:40