http://www.dakkadakka.com/dakkaforum/posts/list/54.page JForum - http://www.jforum.net a) During what percentage of years does Ithaca get more than 40" of rain?
b) Less than how much rain falls in the driest 20% of all years?
c) A Cornell University student is in Ithaca for 4 years. Let represent the mean amount of rain for those 4 years. Describe the sampling distribution model of this sample mean, .
d) What’s the probability that those 4 years average less than 30" of rain?

Having trouble with question "d" not sure what formulas and numbers I need.
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So your initial population is N(m,std). Assuming independent observations the sample mean for those 4 years has a distribution N( m, std/sqrt(n) ), with n=4. Now all you need to do is find z(30) using that sampling distribution. Then you can find P( xbar < 30 inches) ]]> http://www.dakkadakka.com/dakkaforum/posts/preList/584643/6637321.page http://www.dakkadakka.com/dakkaforum/posts/preList/584643/6637321.page GMT