Suppose a 90% confidence interval, based upon a sample of size 35, for the mean number of hours that college students spend on social media each week was 25 to 35 hours. The sample standard deviation from this previous study was 17.9. How many students should be surveyed in order to cut the width of the interval down from 10 hours to 5 hours? Group of answer choices A.100 B.300 C.250 D.139
the 90% confidence interval is = (25,35)
so, the margin of error = (35-25)/2 = 5
given data are:-
margin of error (E) = 5/2= 2.5 [ a you want to cut the width of the interval down from 10 hours to 5 hours...i.e, you have to half the margin of error.]
sample standard deviation (s) = 17.9
z critical value 90% confidence level, both tailed test be:-
the needed sample size be:-
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