A study on trends in cigarette smoking among US adolescents has a sample size of
ID: 2932522 • Letter: A
Question
A study on trends in cigarette smoking among US adolescents has a sample size of 16 000 students from grades 8, 10, and 12. It was found that in the year 2005, 25% of 12th-grade boys and 22% of 12th-grade girls were current smokers, ie. they had smoked at least one cigarette in the past 30 days (Nelson et al., 2008) (a) If a class contains seven girls and eight boys, what is the probability that all students in the class are smokers? (b) If a class contains seven girls and eight boys, what is the probability that none of the students in the class are smokers?Explanation / Answer
a)as probability is independent for being a smoker from person to person
probability that all are smokers =(0.22)7*(0.25)8 =3.806*10-10
b)as probbaility of not being a smoker for a boy =1-0.25=0.75
probbaility of not being a smoker for a girl =1-0.22=0.78
hence probability that all are non-smokers =(0.78)7*(0.75)8 =0.017585
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