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# S2 help please (poisson distributions) Watch

1. It is claimed that 95% of people in a certain village are right handed. A random sample of 80 villagers are tested to see if they are right or left handed. Use a Poisson approximation to estimate that the number of people that are right handed is:

a) 80
b) 79
c) at least 78

So I know at first this is a binomial question...

Im going to use z instead of lambda because I Dont know how to make a lambda on the computer :P So

z = mean = np

so np = z

z = 0.95 x 80 = 76

So And I got a math error (because the numbers are too small for the calculator i presume)

I know its probably easier to use a binomial distribution as n is large but p is not small...but the question says use poisson =/

Where have I gone wrong? Or is the book stupid? :P

Thanks all
2. The only thing I can think of is doing 1 - the probabilities but for left handed so
3. Ok ive jsut tried doing 1-left handed and 80! is a math error...so could you do leflt handed for ?
4. Ok just worked it out...work out P(X=0) for left handed people = P(X=80) right handed

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Updated: November 30, 2010
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