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A poll of 500 randomly selected registered voters was recently administered. Respondents were asked, "Do you approve of President Bush's policies relating to the war in Iraq?" Suppose that we know that 40% of all registered voters approve of the policies.
a) What is the random variable X?
b) Is X binomial? Support your answer.
c) What is the probability that at most 185 voters responded yes to the question?
d) How many voters would you expect to respond yes?

Respuesta :

a. # from sample who responded "yes" 

b. yes/no case, fixed # of trials, independence , p ≈ constant 

c. using a binomial calculator, P[x ≤ 185] = .9219 <------ 

d. E[x] = 500*0.4 = 200 

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