please help me with this!!

#1
The centers for disease control say that about 30% of highschool students smoke tobacco (down from a high of 38% in 1997). Suppose you randomly select high-school students to survey tehm on their attitudes toward scenes of smoking in the movies. what's the probability that

A) none of the first 4 students you interview is a smoker?
B) the first smoker is the sixth person you choose?
C) there are no more than 2 smokers among 10 people you choose?
 

JohnM

TS Contributor
#2
A) 0.7^4
B) 0.7^5 * 0.3

C) find P(0), P(1), P(2) using the binomial formula (see the post in the Examples section) and add them up
 
#3
Oh please help me with this!

Statistics from Cornell's Northeast Regional Climate Center indicates that Ithica, NY, gets an average of 35.4" of rain each year, with a standard deviation of 4.2". Assume that a Normal model applies.

A). During what percentage of years does Ithica 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 Ithica for 4 years. Let y "bar" represent the mean amount of rain for those 4 years. Describe the sampling distribution model of this sample mean, y "bar".

D). What's the probability that those 4 years average less than 30" of rain?