checking maths answers

[mollykins]

Factor, and anyone else good at maths, i've done some stuff but can you check them please, I would get my mum or dad or friend to but; i lost mum and dad with most my work in year 9 and my friends are only doing foundation.

1) these are eqations of lines; (P) y=3x+5 (Q) y=4-3x (R) y+3x=1

a) which is parallel to y=3x ? P and Q

b) which goes through the point (2,7) ? S

c) write down the gradient of y+2x=7 ? +7 (is it necessary to say + ?)


And this at the start of a paper but i always find explaining things hard.

2) mike says that 18% or £840 is equal to 36% of £420

explain why he is correct, do not calculate 18% of £840.

18% is half of 36%. and 840 is double 420.

2 (n/2) = n ?????????? i have no idea if that is right.

3)make t the subject of the formula w=2t+v

-v . . . . . w-v=2t
1/2 . . . . (w-v)/2=t

when doing stuff liek that above, i normally draw a vertical line and and jot down my stages, similar to what i've done there, is that a good idea? When checking back over, its easier to spot mistakes i think and its clear to the examiner what i was doing.

[beejay1124]

hi molly-wot about ye

[factor-fiction]

1.) Only P is parallel. Q has a negative gradient (-3) and is perpendicular to y=3x

[factor-fiction]

1b) What is the equation of line S. Certainly P,Q and R don't pass through those points
1c) No. You can rewrite this as y= -2x +7 so gradient is -2. The 7 is not the gradient- it's where the line intercepts the y axis

[mollykins]

oops, s is y-3x=1

[factor-fiction]

2. Yes.

[factor-fiction]

Back to Q1 then,
If S is y-3x=1 then y= 3x+1.
So for a) S is also parallel to y=3x
And (2,7) does lie on S

[factor-fiction]

3) w=2t+v
so w-v=2t
so 2t= w-v
so t= (w-v)/2
Exactly as you've done it

[mollykins]

:D the last one is the most i'm unsure about.

[mollykins]

I mean the middle one.

[factor-fiction]

Yes, always explain what you are doing. Write each step separately (many pupils just write an endless stream of nonsense calculations such as 1+1=2 x3=6 +100 =106
I suggest you 'tell a story' to the examiner about what you are doing (eg "subtracting v from both sides"), but in your case be careful as I know you can go on a bit sometimes, lol).

[mollykins]

And if i can i lay each stage on a seperate line.

[factor-fiction]

Mike says that 18% or £840 is equal to 36% of £420. Explain why he is correct; do not calculate 18% of £840.

Well you could say 18% of £840 = 840 x 18/100
840= 2 x 420
18 x 2 =36

so 18% of £840 = 840 x 18/100 can be rewritten as 2 x 420 x (36/2)/100

which in turn can be rewritten thus:
2 x 420 x (36/2)/100 = 420 x 36/100.

Now 36% of £420 = 420x 36/100

The two are identical.

But that's a bit long winded isn't it.

If it's worth only one mark I'd go for your explanation- they simply want you to show you know that y% of 2n is the same as 2y% of n

[factor-fiction]

Yes, always put each step on a separate line.

[factor-fiction]

Is that it?
My bill is in the post.

[bibblebub]

could you go through again starting from 'negative gradient'?

[mollykins]

thanks factor [sends cyber hugs and kisses] my maths exams which are 55% of my gcse grade are on monday and friday

[mollykins]

positive gradient goes from bottom left to top right and negative goes from top left to bottom right.

[factor-fiction]

Correct mollykins. I'm sure bibblebub was only teasing and I expect he is pretty good at this stuff- my guess is he has done maths beyond GCSE

[factor-fiction]

AQA module 5 mollykins?

[mollykins]

3 and 5 so we have 2, 90 minute exams monday is non calc and friday is calcs allowed.