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N is large, P is small and what does that mean? watch

1. The questions in the title, but when it says n is large, when does it become large and when it says p is small how about then? This is about the Edexcel S2 when using approximations, I think I remember someone saying n is more than 50 and p is less than 0.1 for those to apply, is that right?

2. what i do is that if np is less than or equal to 10 then u can use tables if not then use normal
3. Thanks.

4. say you have a distribution (X) where X~Po(?) you can approximate this to binomial so long as "n is large and p is small" which basically means that there is a large group for which there is a small probability of an event happening
conditions are generally - n>50 and np (lambda)<5
5. n is large usually means n>30 or n>50 depending on the distribution. (most use n>30)

If you check the tables, you can get a rough idea of which approx to use as binomial doesn't go higher than n = 30 and poisson n = 38.
6. Thanks guys, I think I get what numbers to use now and I've backed up your suggestions from the textbook. Thanks again.

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Updated: June 22, 2004
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