The Centers for Disease Control say that about 30% of high-school students smoke tobacco (down from a high of 38% in 1997). Suppose you randomly select high-school students to survey them 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?