Question

A random sample of state gasoline taxes (in cents) is shown here for 8 states. Round sample statistics and final answers to at least two decimal places.

42.1	61.6	64.1	43.5
43.4	55.5	47.2	39.2

Use the data to estimate the true population mean gasoline tax with 80% confidence. Assume the variable is normally distributed.

Answer 1

the necessary calculation table :-

taxes (x)	x2
42.1	1772.41
61.6	3794.56
64.1	4108.81
43.5	1892.25
43.4	1883.56
55.5	3080.25
47.2	2227.84
39.2	1536.64
sum=396.6	sum=20296.32

sample size (n) = 8

degrees of freedom (n-1) = (8-1) = 7

t critical value for 80% confidence level, both tailed test be:-

[ using t distribution table for df=7,alpha=0.20, both tailed test ]

the 80% confidence interval for the true population mean gasoline tax is:-

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