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# S2 Jan 15

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1. Hi - I have one small problem question on the Jan 15 S2 paper I require a bit of help with!

https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

There's a link to the paper..

It is 6 (d) and the entirety of Q7 I am struggling with - mainly with Q7 I can't understand how it is y is normally distributed with (n/5, 4n/25)???

Thanks!
2. no matter how many questions there are, guessing randomly you're gonna get 1 out of 5 questions right
let n =number of correct questions
the mean number of correctly guessed questions would then b n/5
variance is just the mean*(1-probabilty of success) so n/5 multiplied by (1-0.2) =4n/25
3. (Original post by cheesedrew)
no matter how many questions there are, guessing randomly you're gonna get 1 out of 5 questions right
let n =number of correct questions
the mean number of correctly guessed questions would then b n/5
variance is just the mean*(1-probabilty of success) so n/5 multiplied by (1-0.2) =4n/25
Ahhhhh... thank you!
4. I think it is better put as you having n trials and p = 1/5.

So variance of the binomial is given by np(1-p).

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