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About Vivian
Expertise
I can answer questions on probability, distributions, statistical inference, statistical estimation, hypothesis testing, analysis of categorical data, linear regression, generalized linear regression, ANOVA, and linear mixed models. I cannot answer questions on stochastic processes.

Experience
I have worked as a research assistant at the University of Michigan, Ann Arbor for two years.

Organizations
American Statistical Association

Education/Credentials
University of Michigan, Ann Arbor Master of Science

 
   

You are here:  Experts > Science > Mathematics > Probability & Statistics > Probability question

Probability & Statistics - Probability question


Expert: Vivian - 6/3/2008

Question
Hi,
can you please answer this question?

it rains 40 of the year in Seattle. if 8 days are chosen at random, what is the probability that at most 2 of the days it rained.  Thanks

Answer
The number of the day it rained follows a hypergeometric distribution.

P (at most 2 of the days it rained) = P (0 of the days it rained) + P (1 of the days it rained) + P (2 of the days it rained).

Where P(x of the days it rained) = (40 choose x)*[(365-40) choose (8-x)]/ (365 choose 8)

In general, n choose y = n! /(y!*(n-y)!)


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