Edexcel A2 C4 Mathematics June 2016 - Official Thread

Stupid errors like

$[br]\dfrac{1}{3} \dfrac{-1}{3} [br]$
au lieu of
$[br]\dfrac{1}{3} \dfrac{-2}{3}[br]$basically since 1/2-1 = -1/2, i think 1/3-1=-1/3

Hi, does anyone know if there is a January 2015 IAL S2 paper ?

All of you geniuses already started doing past papers & I'm not even finished the course wait for me loool

All of you geniuses already started doing past papers & I'm not even finished the course wait for me loool

Does anyone do D1? How are you finding it?

C3,C4, yeah? How much do you have left? It's getting kinda late, isn't it?

All of you geniuses already started doing past papers & I'm not even finished the course wait for me loool

Haven't revised it in ages, but most of it is straightforward, there are a few tricky bits, like scheduling without doing gantt charts.

When I approximate from Binomial to Poisson, Binomial to Normal or Poisson to Normal, do I have to change the letter ("X" to a different letter ("Y" ? For instance, X-B(1000,0.01) would be approximated to a Normal distribution, right ? In the markscheme they would put "N(10,10)".
Would it be wrong if I put "Y-N(10,10) ?

Now onto different point. When I Scale up a variable (such as Lamda) do I have to change the letter I first started with ? For example, there are 2 accidents in 1 week so the distribution would be X-Po(2) and I would let X be the random variable the number of accidents. If the question now said in 50 weeks, would I write X-Po(100) or Y-Po(100) ?
Please could someone help clarify this basic point that I can't seem to get :/

In the first case, usually I wouldn't bother to change the variable. Perhaps make it clear it's an approximation. But I also doubt you would lose marks if you said you were approximating X by the variable Y with that distribution, so long as at the end you give your approximate answer in terms of X.

My stats teacher told me that we have to change the variable for your approximation. So suppose you have X ~ B(1000, 0.01), $\displaystyle X\sim \mathrm{B}\left ( 1000, 0.01 \right ) \Longleftrightarrow X\approx Y \sim\mathrm{Po}\left ( 1 \right )$. He even cut marks for not "renaming" the variable. It gets very annoying having multiple variables denoted by different letters.

Maybe someone can correct me here?

When I approximate from Binomial to Poisson, Binomial to Normal or Poisson to Normal, do I have to change the letter ("X") to a different letter ("Y") ? For instance, X-B(1000,0.01) would be approximated to a Normal distribution, right ? In the markscheme they would put "N(10,10)".
Would it be wrong if I put "Y-N(10,10) ?

Now onto different point. When I Scale up a variable (such as Lamda) do I have to change the letter I first started with ? For example, there are 2 accidents in 1 week so the distribution would be X-Po(2) and I would let X be the random variable the number of accidents. If the question now said in 50 weeks, would I write X-Po(100) or Y-Po(100) ?
Please could someone help clarify this basic point that I can't seem to get :/

In the first case, usually I wouldn't bother to change the variable. Perhaps make it clear it's an approximation. But I also doubt you would lose marks if you said you were approximating X by the variable Y with that distribution, so long as at the end you give your approximate answer in terms of X.

In the second case, I probably would change the name (and say what you're doing and what exactly the new variable is).

My stats teacher told me that we have to change the variable for your approximation. So suppose you have X ~ B(1000, 0.01), $\displaystyle X\sim \mathrm{B}\left ( 1000, 0.01 \right ) \Longleftrightarrow X\approx Y \sim\mathrm{Po}\left ( 1 \right )$. He even cut marks for not "renaming" the variable. It gets very annoying having multiple variables denoted by different letters.

Maybe someone can correct me here?

I didn't and it all turned out fine - but tiny hobbit also suggested the change of variable too, so I'd go with that.

What I used to do was $X \sim B(1000, 0.01) \Rightarrow X \approx \mathrm{Po}(1)$

It wouldn't matter as far as marks go (I'm talking Edexcel here). The important thing is that you are clear as to which variable you are using at any given moment and what its distribution is. If using a different letter keeps it clear for you, then that's a good thing.

Thank you!

I have another (possibly silly) question: on the paper, you're always asked to state your hypotheses clearly. Does this make it alright to just simply state $p= 0.25$ or do we have to write everything out in words?