Edexcel S2 - 27th June 2016 AM

Please could someone explain question 7d on here https://57a324a1a586c5508d2813730734691051ac35fd.googledrive.com/host/0B1ZiqBksUHNYZ3M4QzJ0N19IeHc/June%202014%20(R)%20QP%20-%20S2%20Edexcel.pdf have never been able to understand it, thanks

Up to which point do you understand?

It starts with E(R) = E(aX^2 + bX) = aE(X^2) + bE(X) using laws of expectation.

Ah okay thank you, I understand how you find E(X) and Var(X) but I'm stuck from there, thanks

So you know that (from my previous post) you are trying to find E(X^2) and E(X) and multiply them by a and b respectively and sum them to find E(R). And you know that, by the definition of Var(X), Var(X) = E(X^2) - E(X)^2, so E(X^2) = Var(X) + E(X)^2, and since you can work out those two things you can find E(R).

Does anyone know where I can find the s2 edexcel 2015 paper? I can't find the link to it anywhere. Thanks in advance!

Hey, can someone help me?

Is it neccessary to learn the the proof for the E(X) and Var(X) for Continuous Uniform Distribution (Rectangular Distribution)?

Bad news: well, I've seen it pop up in a past paper once.

Good news: You don't need to remember it. It's essentially all in your formula book.

Can you see the bit in the "PDF is $\frac{1}{b-a}$" thing? And then above that table is "Expectation/mean is $\int xf(x) \, \mathrm{d}x$" and the corresponding thing for $\text{Var}(x)$?

So all you need to do is, if you're asked to prove it, you don't need to remember anything. Open your formula booklet, they tell you the pdf is $f(x) = \frac{1}{b-a}$, they want you to find the E(X), okay then, just plug it into the formula given:

$\displaystyle E(X) = \int xf(x) \, \mathrm{d}x = \int_a^b \frac{x}{b-a} \, \mathrm{d}x = \frac{1}{a-b} \int_a^b x \, \mathrm{d}x$ which you can finish up from here.

And they want variance, okay then, still just plugging in:

$\displaystyle \text{Var}(X) = \int x^2 f(x) \, \mathrm{d}x - \mu^2 = \int_a^b \frac{x^2}{b-a} \, \mathrm{d}x - \mu^2 = \frac{1}{b-a} \int_a^b x^2 \, \mathrm{d}x - \mu^2$

Where $\mu$ is just the expectation you found above.

For the expectation:

Hey, can someone help me?

Is it neccessary to learn the the proof for the E(X) and Var(X) for Continuous Uniform Distribution (Rectangular Distribution)?

Hey, can someone help me?

Is it neccessary to learn the the proof for the E(X) and Var(X) for Continuous Uniform Distribution (Rectangular Distribution)?

Bad news: well, I've seen it pop up in a past paper once.

Good news: You don't need to remember it. It's essentially all in your formula book.

Why does everyone say S2 is easy?

Because it is?

Learn... I'm not sure.

You can/should probably know how to get it by using definitions to find E(X^2) and E(X) and using that Var(X) = E(X^2) - E(X)^2, The one tiny bit that you need to know is that $b^3 - a^3 = (b-a)(a^2+ab+b^2)$ - that's the hardest bit and the rest is okay.

Hope you're finding everything okay

I think I may be screwed for S2.

I only know DRV + Estimation/sampling. Even then I only get 9/14 -> 10/15 marks on average.
Why does everyone say S2 is easy?

You will be fine! I was so pissed off at myself for leaving S2 revision till so late. But it's such a small module and easy to grasp. The ExamSolutions dude does a great job at explaining it. If you need any help for S2 feel free to ask me, it would be practise for me too.

Spend like a day on the other three topics you have left, and I promise you it will take you only a day to go over it all.

Help please



Posted from TSR Mobile

Help please



Posted from TSR Mobile

Seems like you're going to be doing simple unitary stuff. i.e. 1 customer in 6 minutes, so 10 customers in an hour. For the second part, think of a suitable approximation when a Poisson distribution becomes difficult to apply.