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# help with AS maths S2 ? Watch

1. OK so it's question 2 that im stuck on. The question always starts with using a suitable distribution ...
It's OCR MEI .
http://www.mei.org.uk/files/papers/S2_2014_June.pdf 2 (vi) how do i know if its X - N(n,p) or Normal(...) ?
2. Mr Statistics Pro somebody needs your help.
3. (Original post by CountTesla)
OK so it's question 2 that im stuck on. The question always starts with using a suitable distribution ...
It's OCR MEI .
http://www.mei.org.uk/files/papers/S2_2014_June.pdf 2 (vi) how do i know if its X - N(n,p) or Normal(...) ?
Takes practice. *usually* the words average rate suggest Poisson

Also, theoretically the poisson can go up to very high numbers (like 1,000,000) but the probability of that is.. 0, or as close to 0 as you can get (use P(X=1 million) for a poisson distribution with a rate of like 10 ), but in this situation it would make sense if you had say 100 defects in 1 square metre, whereas it wouldn't make sense in another situation, whereas if you had 100 people in a town, you thought the probability of winning the lottery was 1 in 100 and 5 people one it, it wouldn't make sense to use poisson as you could have (a very, very, very low chance) of having 150 winners out of 100 people.
4. (Original post by SeanFM)
Takes practice. *usually* the words average rate suggest Poisson

Also, theoretically the poisson can go up to very high numbers (like 1,000,000) but the probability of that is.. 0, or as close to 0 as you can get (use P(X=1 million) for a poisson distribution with a rate of like 10 ), but in this situation it would make sense if you had say 100 defects in 1 square metre, whereas it wouldn't make sense in another situation, whereas if you had 100 people in a town, you thought the probability of winning the lottery was 1 in 100 and 5 people one it, it wouldn't make sense to use poisson as you could have (a very, very, very low chance) of having 150 winners out of 100 people.
So when n is large and p is small use poisson but when similar then Normal() ?
5. (Original post by CountTesla)
So when n is large and p is small use poisson but when similar then Normal() ?
Oh, I seem to have misunderstood your question - sorry!

If n is such that it can't be read off the tables then that is usually when you go to normal. (Are you allowed to approximate a poisson with a binomial in OCR, or are you thinking of the other way around?)
6. (Original post by SeanFM)
Oh, I seem to have misunderstood your question - sorry!

If n is such that it can't be read off the tables then that is usually when you go to normal. (Are you allowed to approximate a poisson with a binomial in OCR, or are you thinking of the other way around?)
Yeah
7. Our S2 is pretty nice tbf.

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