A class of two hundred students took a calculus final. If the sample mean for thirty randomly selected students was 95 percent with a (sample) standard deviation of 6.6 percent, construct a 99% confidence interval for the mean score of all students. Show all work, including the formula you are using.
Solution :
Given that,
Point estimate = sample mean = = 95
sample standard deviation = s = 6.6
sample size = n = 200
Degrees of freedom = df = n - 1 = 199
At 99% confidence level the t is ,
t /2,df = t0.005,199 = 2.601
Margin of error = E = t/2,df * (s /n)
= 2.601 * (6.6 / 200)
= 1.214
The 99% confidence interval estimate of the population mean is,
- E < < + E
95 - 1.214 < < 95 + 1.214
93.786 < < 96.214
(93.786 , 96.214)
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