A sample of 26 elements from a normally distributed population is selected. The

Question

A sample of 26 elements from a normally distributed population is selected. The sample mean is 10 with a standard deviation of 4. The 95% confidence interval for population mean is

a) 6.000 t0 14.000
b) 9.846 and 10.154
c) 8.384 to 11.616
d) 8.462 and 11.538


A random sample of 25 statistics examinations was taken. The average score in the sample was 76 with a variance of 144. Assuming the scores are normally distributed, the 99% confidence interval for the population average examination score is
a) 70.02 to 81.98
b) 69.82 to 82.18
c) 70.06 to 81.94
d) 69.48 to 82.52
a) 70.0

Explanation / Answer

You can do either do this problem by hand or with a calculator. The easiest way is to use a TI-83 or TI-84. On a TI-83/84 hit STAT then select TESTS. Choose 7:TINTERVAL. Selects Stats as input method and type in the given statistics. This is what you should see on your calculator screen:

TInterval

Inpt: Data Stats

x bar: 10

Sx: 4

n: 26

C-Level: .95

Calculate

Then select Calculate and you get (8.3844, 11.616) as your confidence interval. Therefore the answer is c.

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