Edexcel S2 - 27th June 2016 AM

a. b = 23/6

b. k = 2

c E(X) = 1.39. E(X^2) = 2.70. Var(X) = 0.77. Deviation = 0.88 (answers within that range, depending on rounding etc)

d. IQR question removed - takes too much time.

e. 0.69.






Well done the last bit should be 2 s.f but doesn't matter really. Just something to be wary of in the exam if they specify how many s.f you need.

Sean explained the first part to before. I thought I understood it but still managed to get the last part of the question wrong.

I did 1 - (225)/(t+15)^2 = 0.1

Can someone explain to me why its wrong. If you can make the explanation really simple, even child like. It would be really helpful

Not necessarily - I think it's just a method mark (hence the M) for having the 'right method'. The cao means 'correct answer only' so that's where the two methods will be differentiated - the one where it has been applied to the right one will get you that A1 mark.

Consider both sides of the rectangle:
Look at the method used for question 11:

http://www.madasmaths.com/archive/maths_booklets/statistics/rectangular_distribution.pdf

Do we need to know any proofs? I heard we need to know how to prove the variance of a uniform distribution... is this correct?

I hope it is not too much trouble, but please could someone explain how they think through some questions to help my understanding!


1b)


2c)

and



7d)

Thank you very much in advance!

Consider both sides of the rectangle:
Look at the method used for question 11:

http://www.madasmaths.com/archive/maths_booklets/statistics/rectangular_distribution.pdf

Is this the last A level exam in general? From the people I know S2 is last. 27th June is damn late... Can't believe how quick college flew by. Seems like yesterday I was going to open days.

hey man do you mind explaining the first part for me

A distribution X is used to model the length, in mm, of the first tear of a uPhone charger, and the PDF is specified below. However, Wapple have been careless and have lost some key details of the PDF.

$kx(1-x)$ if $0 \leq x < 0.5$

$\frac{23}{40} - \frac{3x}{20}$ if $0.5 \leq x \leq b$

0 otherwise.

a) Given that b is the minimum value greater than 0 such that f(b) = 0, find the value of b.

I have a question about the S2 exam tomorrow, so I was doing past papers and some questions ask you to work E(X^2) for a CDF yet, solutions show the answer being gathered from the VAR(X) formula in the S2 formula booklet. Do you use the Var formula in the booklet for E(X^2) or am I nuts??

I have a question about the S2 exam tomorrow, so I was doing past papers and some questions ask you to work E(X^2) for a CDF yet, solutions show the answer being gathered from the VAR(X) formula in the S2 formula booklet. Do you use the Var formula in the booklet for E(X^2) or am I nuts??

So the b is the upper limit of the second part of the pdf. (f(x)).

You are told that, after 0 (since f(0) = 0) b is the first value such that f(b) = 0.

You automatically know that b is greater than 0.5, otherwise the pdf would not make sense, so you have to look at the second part and realise that the PDF in that part is a decreasing function, so there will come a point where f(x) = 0, and that x will be b. After f(x) is 0, you go past b, it doesn't become negative as you'd expect - it actually becomes 0, because after b, any x value falls into 'otherwise' so the graph flatlines. So you're looking for b, the y intercept.

So that happens when
$\frac{23}{40} - \frac{3b}{20} = 0 \Rightarrow b = \frac{23}{6}$

Kind of hard to see to be honest. But don't worry, I don't think you'd get asked something like that, particularly in S2 - it's more like C3 stuff.

Along with FP3 it is one of the last A level maths exams, however I believe there is a physics exam the day after.

Hope this helps mate!

Appologies for hand writing.

https://gyazo.com/af6ccadea92e33a2fa1cc2830439e94d
https://gyazo.com/082b793a25a8162518a2bf5585ed8183