A consumer affairs investigator records the repair cost for 1010 randomly selected VCRs. A sample mean of $72.82 and standard deviation of $24.17 are subsequently computed. Determine the 90% confidence interval for the mean repair cost for the VCRs. Assume the population is approximately normal.
1: Find the critical value that should be used in constructing the confidence interval. Round your answer to three decimal places.
2. Construct the 90% confidence interval. Round your answer to two decimal places.
Answer
(A) given that we have to find 90% confidence interval
so. alpha = 1- confidence level
= 1-0.90
= 0.10
and
degree of freedom = n-1
= 10-1
= 9
t critical = T.INV.2T(alpha,df)
= T.INV.2T(0.10,9)
= 1.833
(B) using TI 84
press stat then tests then TInterval
enter data
x = 72.82
s = 24.17
n = 10
c-level = 0.90
press enter, we get
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