anyone good with how marking works in edexcel maths?

I did a question today and not sure how many marks I would have scored.

It would be nice if someone with good knowledge of the marking system came forward and helped me. I will post the question. It's quite long and I have no idea of the exact expressions used. It involved no absolute values.

Reply 1

thekidwhogames

An Edexcel question that's long? Is it a past paper?

Reply 2

RickHendricks

Original post by thekidwhogames

An Edexcel question that's long? Is it a past paper?

I don't know for sure. However it involved areas and differentiation.

Basically it gave us a expression for the area of a shape in terms of pie and r (where r was the radius of one of the circles in the shape)

Then it told us to show that the maximum area was a expression which they gave us.

To do that, I had to differentiate, and work out the value of r for which it is maximum. I differentiated it correctly, however used a wrong value of r. Would this mean my marks would be penalized?

IT was 5 marks in total.

I differnetiated correctly
I proved it was maximum
I used incorrect r value
My next workings took me now here (i simplified it much as possible)
My final proof could not be done

How many marks would i get?

Reply 3

RickHendricks

Original post by thekidwhogames

An Edexcel question that's long? Is it a past paper?

so?

Reply 4

thekidwhogames

Original post by RickHendricks

I'm assuming it was one of those questions asking to find an area and prove it's maximum? Therefore, to get all 5, you need to differentiate the function correctly and set dy/dx=0. You will then need to find d^2y/dx^2. Solve dy/dx=0 and if you get 2 solutions; plug both into the 2nd derivative and then deduce which value of r gives the maximum value of the area (e.g. when f'(x) < 0)).

If you had the correct area and everything but wrong value of r, you'd lose a maximum of 2 but you'd probably lose 1. I'm not too sure on how this little mistake would get penalised.

Reply 5

RickHendricks

Original post by RickHendricks

@Notnek

Sorry to disturb you, but you got any clue?

Reply 6

Notnek

Original post by RickHendricks

Can you please explain what you mean by "used a wrong value of r"? Maybe use an example - it doesn't have to be the exact question you did.

Reply 7

RickHendricks

Original post by Notnek

Can you please explain what you mean by "used a wrong value of r"? Maybe use an example - it doesn't have to be the exact question you did.

ok so say we have to differentiate A = pieR^2 + 2R

dA/dR = 2pieR + 2

so let that equal 0, meaning we get 2pieR + 2 = 0

Therefore R = -1/pie

However I put down 1/pie instead.

This meant that I could no longer get to the statement they told us, since i got a wrong value of R, because if i subbed in my value to the A, I can never get to the same equation they got to.

However I was able to prove it's maximum since it's linear and dA^2/d^2R gave me a single value below 0

These were not the exact values but it's the pattern in which I got my values.

Reply 8

Notnek

Original post by RickHendricks

You made a mistake in the middle of your working and didn't reach the required answer so that sounds like 3/5. But I don't have much confidence with that since I haven't seen the actual question. Also, the problem with making mistakes in the middle of working is that it can make the question easier so it can be very hard to predict how the marks will be laid out. Plus I'm not sure if showing that it is a maximum would get you a mark - I'd need to see the question.

By the way, the greek letter is spelt "pi" not "pie".