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# Edexcel S2 - 27th June 2016 AM

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Very easy
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1. (Original post by Abc321zxc)
can someone check june 2006 question 7a and tell me why it is a binomial and not a poisson?>

A binomial distribution usually implies a cap. Whereas with Poisson, like measuring rate of customers, theoretically there is no cap on the number of customers that could come in a period of time. The binomial for example is different, because if you're tossing 20 coins it is impossible to get 25 or 30 heads, something that a poisson distribution would imply.
2. Tomorrow will probably be the hardest S2 with lots of conditional probabilities and in-context uniform distribution.
3. (Original post by Abc321zxc)
can someone check june 2006 question 7a and tell me why it is a binomial and not a poisson?>
1 in 5 bowls so you have a p

25 bowls so you have an n
4. (Original post by Student403)
If anyone feels **** about tomorrow, just remember I started revision an hour ago

I think that would be some consolation if you weren't the Student403
5. Part (c): can anyone explain why {[P(X = 1)P(X = 3)] intersection P(X = 4)} becomes P(X = 1) × P(X = 3) here?

6. (Original post by SeanFM)
I think that would be some consolation if you weren't the Student403

7. SeanFM

For the last part of this question I integrated from 1.5 to 2.5. However in the mark scheme they did 1 - integral 1.5 to 2.5. Do you know why?
8. I just thought, in questions where we are given functions (pdf or cdf), is it possible to get trigonometry? Such as f(x) = sinx over a specific interval?

We usually get quadratic or cubic equations, but is it still possible?
9. can someone explain this

say if ive got an observed value of x= 4

but critical values are

x<3 x>12

what does that tell me?
10. (Original post by Ayman!)
Part (c): can anyone explain why {[P(X = 1)P(X = 3)] intersection P(X = 4)} becomes P(X = 1) × P(X = 3) here?

that doesn't quite make sense as far as I can see.

Something like where the X1 + X2 disappears because it is implied/true by the other statement.

by independence would make more sense.
11. (Original post by SeanFM)
that doesn't quite make sense as far as I can see.

Something like where the X1 + X2 disappears because it is implied/true by the other statement.

by independence would make more sense.
Brilliant! Thank you.

I just intuitively jumped to the next step and got the answer, but needed to see why it worked.
12. (Original post by Armpits)
Tomorrow will probably be the hardest S2 with lots of conditional probabilities and in-context uniform distribution.
What do you mean by in-context uniform distribution?
13. (Original post by taysc)

SeanFM

For the last part of this question I integrated from 1.5 to 2.5. However in the mark scheme they did 1 - integral 1.5 to 2.5. Do you know why?
Because the integral finds probability of being between those two numbers, when you want it to be on either side of those numbers, if that makes sense.
14. (Original post by taysc)

SeanFM

For the last part of this question I integrated from 1.5 to 2.5. However in the mark scheme they did 1 - integral 1.5 to 2.5. Do you know why?
You are looking for the probability of waiting either less then 1.5 or more than 2.5
15. For continuous uniform distribution e(x) is the same as the median and the mean?

SeanFM
16. (Original post by taysc)
What do you mean by in-context uniform distribution?
https://ef8b5216a7366459ac0f2ce0ac13...%20Edexcel.pdf

Like question 3
17. (Original post by NoahMal)
For continuous uniform distribution e(x) is the same as the median and the mean?

SeanFM
It would make sense, yes
18. These are not my favourite questions at all
19. Is it correct that P(Y> or equal to 7.3) for a binomial distribution would be the same as P(Y> or equal to 8)? Thanks
20. (Original post by SeanFM)
Because the integral finds probability of being between those two numbers, when you want it to be on either side of those numbers, if that makes sense.
Yes it does the thank you

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