Algebra

[jukeboxjive]

Here is one gor the egg heads out there.. 5-q=7 what is q and why?

[ChuckFickens]

Really???

q is -2

subtract -2 from 5 and you get 7

[sophie_1003]

q would be -2 not too sure of proper mathematical explanation but that's the answer!

[jd_here]

q = -2 because a minus minus gives a positive.....so there!!

[Prudie]

Not meaning to demote the previous correct answers but egghead not really required to solve that.

[sophie_1003]

That explanation is a bit simplistic jd as it doesn't work in all situations (or so my maths lecturer tried to explain to me!)

[sandyRoe]

is q -12? 2 minuses give a plus

[Whickerman]

all my maths education would disagree - I'm sure there's some obscure reason in some odd theory where q wouldn't = -2 but it fits here.

5 - (-2) = 5 + 2 = 7

[ChuckFickens]

I agree, prudie, Hence the really???

This is primary school level maths.

[factor-fiction]

Well sandyroe, if q were-12 then the expression on the left would be 5-(-12) which would be 17 so that doesn't work.

[sandyRoe]

I got that wrong. I suppose that's one reason why I lost my job at the Treasury

[sophie_1003]

Aww prudie; I thought I'd suddenly got really good at difficult maths!
Was that aimed at what I'd said Whickerman? If yes it was the general rule of 'two minuses make a plus' that my maths lecturer had an issue with because it causes confusion in some situations; for example when adding two negative numbers people apply the 'rule', ignoring the operation and get a positive answer (I think this is what she was getting at anyway!)

[Whickerman]

aaah - gotcha. I suppose that people don't get taught the BODMAS sequences so the lecturer possibly tried to find a way round?

[factor-fiction]

Some primary schools may cover this, chuck, for the top sets in year 6, but now this is a typical sort of question on the Maths GCSE paper and is levelled as around grade E.
The concept of subtracting negatives is quite a difficult one for many pupils to visualise (the best way is probably to think of bank accounts and taking away an overdraft, or temperatures and taking away an ice cube), Also of course the use of letters throws many people who just can't follow the concept.
An even more difficult concept to explain is multiplying by a negative number.

[NazNomad]

I did this in Primary School in the early 70's

[Whickerman]

mee too I'm afraid. That said, my daughter did too, in the late 90s

[sophie_1003]

I'm not sure; think she is just a bit cautious with 'rules' because if they're not taught properly in the first place they cause huge confusion later when the rule has become cemented in a person's memory (a bit like 'I before E except after c') Funnily enough I was taught BODMAS but had completely forgotten what it meant but remembered '2 minuses make a plus'!

[sophie_1003]

Also just to clarify, algebra is taught in Key Stage 2, i.e. Year 3-6 in primary school, can't find particular reference to negative numbers in the National Curriculum but we have been taught methods for teaching the concept to primary children so may be that I just can't put my finger on it at the moment.

[R1Geezer]

a minus minus a minus does not always result in a positive answer but it is the same as adding so. 5-(-2) = 7 but -5-(-2)=-3 ie the -(-2) =+2

You imagine it on a number line:
-7 -6 -5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 +6 +7

then 5-(-2) says start at +5 and move to the left minus 2 times, ie two negative moves to the left = 2 moves to the right, which = +7 see?

similarly -5-(-2) means the same but starting at -5, hence = -3

Geddit?

[sophie_1003]

Ooh good use of a numberline to explain a tricky concept, will keep that in mind R1Geezer!