GCSE Maths que from today...

hellarda · 6 Jun 2011 at 19:39

hello

could someone help me with this maths question that was in the IGCSE paper today? spent ages on it, and couldnt get anywhere :/

(please excuse my paint skills)

taa

Destination · 6 Jun 2011 at 19:52

-edit
worthless without maths symbols

going to do this properly in a fashion it can be read

hellarda · 6 Jun 2011 at 20:02

Hikari Kisugi said:
Going to use x for the Pi symbol as i can't see it on my machine.

2xr^2 + 2xrh
------------ =2
4xr^2

Expanding and then substituting and cancelling
2xr(r+h) .......... r+h
--------- = --------- = 2
4xr(r) ................. r

h/r=2 h=2r

Then for the second part of the fun

xr^2h
-------- = the answer y
4/3xr^3
so using h=2r
3xr2(2r)...... 3(2r) .......... 6
--------=---------= ------ =1.5
4xr^3.......... 4r .............. 4

I think.

excellent, didnt get any of the working, but if you're right i guessed 4, so that was an incredibly amazing guess

and the pie symbol was copied from google

interesting to see if anyone else gets a different answer?

Valentino · 6 Jun 2011 at 20:02

I make h=3r not 2r.

p4radox · 6 Jun 2011 at 20:07

I suppose you need to define h for the cylinder then eliminate it?

Valentino · 6 Jun 2011 at 20:07

(2*pi*r*h + 2*pi*r^2)/4*pi*r^2 = 2
=> (2*pi*r*h/4*pi*r^2)+(2*pi*r^2/4*pi*r^2)=2
=>(h/r)(2*pi*r/4*pi*r) + (2*pi*r^2/4*pi*r^2)=2
=>(h/r)(1/2) + 1/2 = 2
=>h/2r + r/2r = (h+r)/2r = 2
=>(h+r) = 4r => h=3r.

Haven't gone through the rest yet though.

Destination · 6 Jun 2011 at 20:08

hellarda said:
excellent, didnt get any of the working, but if you're right i guessed 4, so that was an incredibly amazing guess

and the pie symbol was copied from google

interesting to see if anyone else gets a different answer?

The answer I actually got was 1.5
Its just utterly unreadable given the forum layout
I will try to lay it out in better fashion

God GCSE maths was 20 years ago now :/

-edit worse than that, i also managed to do it wrong, lol, oops

Valentino · 6 Jun 2011 at 20:12

paradox has done it right in nice latex too.

Seems quite complicated for a GCSE tbh.

Might just be because i've forgotten the algebra of geometry, things like the area of a circle i had to deduce from the fourmulas given rather than just knowing it as a GCSE student does. Other than that though it is just simple manipulation using algebra.

Scon · 6 Jun 2011 at 20:14

Valentino said:
Platypus has done it right in nice latex too.

Seems quite complicated for a GCSE tbh.

It's an iGCSE, apparantly much harder.

i being international

SpeedFreak · 6 Jun 2011 at 20:17

Use the surface area to determine the value of h in terms of r and then substitute. I make the answer 9/4

edit: as shown above

Nerusy · 6 Jun 2011 at 20:17

I got h=3r

thus the answer is 9/4 or 2.25

hellarda · 6 Jun 2011 at 20:25

p4radox said:
I suppose you need to define h for the cylinder then eliminate it?

ahh that looks about right.

shame i couldn't think of that in the exam

yes it was quite a challenging paper... but i only missed that one out, and i know i did one other rong but meh.

yeh the Igcse is harder, and less coursework based too, tbh i prefer less coursework, although it means i have 18 exams

half way there now! 9 to go...

Valentino · 6 Jun 2011 at 20:28

burrell said:
It's an iGCSE, apparantly much harder.

i being international

Well that explains it then. It puts our education system to shame tbh, of what I've seen of the math side of it anyway.

Just looking at the specimen paper

http://www.cie.org.uk/docs/dynamic/31227.pdf

I wonder how many grade C GCSE students could even do the first question correctly lol.

GreatAuk · 6 Jun 2011 at 20:28

All you need to do is sub in the formulae correctly and cancel it all out. I get the 9/4 answer as P4radox.

2= (2pi r h + 2pi r^2)/(4pi r^2) = (h + r)/(2r)
so: h + r = 4r, h = 3r
then:
ratio = (3pi r^2 h)/(4pi r^3) = (3h)/(4r)
sub in h = 3r
ratio = (3*3r)/(4r) = 9/4

edit: But although this kind of question does seem rather easy to me now, I suppose it's these core skills that need to be built to do A-level maths, even if at A-level maths is a slightly different subject (imo). This question is quite a good test of whether a candidate can cancel and substitute effectively.

hellarda · 6 Jun 2011 at 20:33

Valentino said:
Well that explains it then. It puts our education system to shame tbh, of what I've seen of the math side of it anyway.

Just looking at the specimen paper

http://www.cie.org.uk/docs/dynamic/31227.pdf

I wonder how many grade C GCSE students could even do the first question correctly lol.

hmm thats a different board to what we do, we do edexcel IGCSE, that CIE paper looks slightly harder, but not impossible

Six7th · 6 Jun 2011 at 20:33

Got 9/4 too. Some A-level stuff is easier than this!

hellarda · 6 Jun 2011 at 20:37

Six7th said:
Got 9/4 too. Some A-level stuff is easier than this!

yeh exactly... I actually did the paper last year too, but missed the A* by 0.5% :/ even after a remark :mad:

so the school made me retake this year.

AS WELL as doing the ADD maths course, which is all algebra, and I have that exam on Monday, apparently some of it is harder than A level stuff.

got 13% in my mock for that :cool:

hopefully the paper on friday for gcse will be easier :/

SpeedFreak · 6 Jun 2011 at 20:54

They made you retake after getting an A :confused:

hellarda · 6 Jun 2011 at 20:56

SpeedFreak said:
They made you retake after getting an A

mhm.... :/ really annoyed me.