Please show your work. a) About 50% of male internet users aged 18-34 visit an a
ID: 3294611 • Letter: P
Question
Please show your work.
a) About 50% of male internet users aged 18-34 visit an auction site (such as eBay) at least once a month. A random sample of 12 male internet users aged 18-34 is taken. What is the probability that at least 8 of the 12 have visited an auction site in the past month?
b)The Helsinki heart study asked whether the anticholesterol drug gemfibrozil reduces heart attacks. They gave the drug to 2000 men aged 40-55 and a placebo to another 2000. The probability of a heart attack for men this aged in a 5-year period is 0.04. What are the mean and standard deviation of the number of heart attacks that will be observed in one group if the treatment does not change the probability?
Explanation / Answer
(a) Here p = 0.50
Sample size n = 12
si it is a binomial distribution.
Pr (X >=8 ; 12; 0.50) = Binomial (X >=8; 12; 0.50)
= 0.1938 [ from binomial table]
(b) sample size of the group = 2000
p = 0.04
Mean of the heart attacks = np = 2000 * 0.04 = 80 people
Standard deviation of the number of heart attacks = sqrt [p * (1-p) * N] = sqrt [ 0.04 * 0.96 * 2000]= 8.76 people