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# Edexcel S2 - 27th June 2016 AM

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1. (Original post by keres)
SeanFM

Hi was wondering if you could help me out.
Attached the question.

Just wondering, is 225/(t+5)^2 a PDF or NOT a pdf? Because if it was a pdf, surely you would need ot integrate to work out the question.

Confused on the whole question tbhAttachment 556323
Ah yes, I remember this question

It is not a PDF. It has a relationship with the CDF though, which is what you have to work out.

Read the line 'the probability that the mosquito survives for 'more than t days is...' and then think about what the CDF is (hint: less than or equal to is the key word for a CDF).
2. (Original post by mehtj006)
Hi everyone, just wanted to ask if i can have this split C1234 D1 S2 FP12 S3 S1 M1 M2
I'm not sure if works slightly differently for IAL, but for normal maths, in A-level maths you can only have a 1 and a 1 (two different types) or a 1 and a 2 of the same type. So D1 and S2 isn't allowed - if S2 goes to A-level maths, S1 must also go to A-level maths.

But the exam board works out how your grade works and makes it the best it can in both, basically.
3. I predict definitions will come up. Also this paper is going to be more challenging than usual, edexcel are increasing the difficulty of m2 and s2 as too any people are getting A's even if they cant do C3 or C4 maths to even B standard!
4. http://qualifications.pearson.com/co...-June-2014.pdf

Can someone explain Q6c, and Q7c-e, please? I obtained all other marks but these ones are bugging me.
5. Need help on 2015 paper q3b anyone know??
6. Does anyone know how to do 3b on 2015 paper please I know it's super easy but I've forgotten how to find the mode :/
7. What are the hardest ever questions from normal papers of s2?

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8. (Original post by Superbubbles)
Does anyone know how to do 3b on 2015 paper please I know it's super easy but I've forgotten how to find the mode :/
sketch the graph. see where the highest point is. The x value of where the point is, thats your mode.
9. Hi Sean,

I really don't understand this question at all. Its from the Jan 13 paper, I was wondering if you could please help with it? I don't get how they set up the F(x) function and so I misunderstood the rest of the question

Thanks SeanFM
10. (Original post by taysc)
Hi Sean,

I really don't understand this question at all. Its from the Jan 13 paper, I was wondering if you could please help with it? I don't get how they set up the F(x) function and so I misunderstood the rest of the question

Thanks SeanFM

(Original post by SeanFM)
Ah yes, I remember this question

It is not a PDF. It has a relationship with the CDF though, which is what you have to work out.

Read the line 'the probability that the mosquito survives for 'more than t days is...' and then think about what the CDF is (hint: less than or equal to is the key word for a CDF).

See post above
11. (Original post by AlphaArgonian)
http://qualifications.pearson.com/co...-June-2014.pdf

Can someone explain Q6c, and Q7c-e, please? I obtained all other marks but these ones are bugging me.
With the CDF, you can find the proportion of children whose estimate is ... blah blah blah.

So that's the proportion (or probability, if you like) of children that are right.. and you have 80 people, so you would expect ... many to be right out of 80.
12. (Original post by SeanFM)
See post above
P ( X > T) = 1- P ( X ≤ T)

Is that what it means?

It still kind of confuses me

13. (Original post by taysc)
P ( X > T) = 1- P ( X ≤ T)

Is that what it means?

It still kind of confuses me

Precisely.

If we take a discrete distribution (no difference if it's continuous, but let's keep it simple), say X is a binomial distribution with p = p (some probability, doesn't matter, n= 20, say).

And we pick a random number in that distribution, say 8. Then every number that the distribution can take (ranging from 0 to 20) is either going to be greater than 8, or less than or equal to 8. It sounds obvious/strange but we can use that. There is no value that X can take that isn't less than or equal to 8, or greater than 8, so as those two statements cover every number in X. You can generalise that for any x value from X,
14. (Original post by bat_man)
sketch the graph. see where the highest point is. The x value of where the point is, thats your mode.
Is sketching the graph the only way to do it? It's only 1 mark
15. (Original post by Superbubbles)
Is sketching the graph the only way to do it? It's only 1 mark
Please link the question in the future it saves everyone else some time

A graph of the pdf is one way of finding the mode. The other (albeit the same idea) is finding the x value for which the pdf takes the highest value, because that value has the highest chance of occuring so in a sample, you'd expect it to be the most common number (the mode). Sometimes you can spot this from the PDF without any calculations.
16. Would you guys reccomend revising s1 before this exam? Did it last year but fair to say I don't really remember much of it. Done alright in s2 papers but I feel like edexcel could easily slip a question that requires s1 knowledge in this year
17. (Original post by Superbubbles)
Is sketching the graph the only way to do it? It's only 1 mark
sketching the graph is really easy. it should take less than a minute. It also allows you determine whether the mode is a stationairy point, where youd have to differentiate the pdf, and set it equal to 0, to find out the mode that way. But yeah, thats the only way i think.
18. (Original post by zombaldia)
Would you guys reccomend revising s1 before this exam? Did it last year but fair to say I don't really remember much of it. Done alright in s2 papers but I feel like edexcel could easily slip a question that requires s1 knowledge in this year
its probably good for maybe a probability type question, or a skew question. Im lucky that i resat s1 this year lol.
19. (Original post by zombaldia)
Would you guys reccomend revising s1 before this exam? Did it last year but fair to say I don't really remember much of it. Done alright in s2 papers but I feel like edexcel could easily slip a question that requires s1 knowledge in this year
Maybe a recap on skew (somewhere in the back of my mind says it's been asked in S2 before, but not sure on that one).

Also the definition of conditional probability - specifically something like this: where X is a distribution, t is some time (that X depends on) and h is a positive number)

. The key bit being that X > t +h intersect X > t is X > t + h, as that is the 'tighter' of the two inequalities.

I haven't defined x, t and h etc but you'll see if it if it comes up (and it has done in one or two past papers).

Lastly, the normal distribution if you aren't at all confident with it, but it can come from doing practice in S2 instead.
20. (Original post by bat_man)
its probably good for maybe a probability type question, or a skew question. Im lucky that i resat s1 this year lol.
Yeah I guess that is lucky in a way

(Original post by SeanFM)
Maybe a recap on skew (somewhere in the back of my mind says it's been asked in S2 before, but not sure on that one).

Also the definition of conditional probability - specifically something like this: where X is a distribution, t is some time (that X depends on) and h is a positive number)

. The key bit being that X > t +h intersect X > t is X > t + h, as that is the 'tighter' of the two inequalities.

I haven't defined x, t and h etc but you'll see if it if it comes up (and it has done in one or two past papers).

Lastly, the normal distribution if you aren't at all confident with it, but it can come from doing practice in S2 instead.
Okay, thanks. I'll just try to do all the past papers over this weekend

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