Question

Construct a 90% confidence interval of the average gasoline price per gallon based on a recent sample of 48 stations. The sample mean was $2.63. Assume the population std deviation is $0.31

Answer 1

Solution :

Given that,

Sample size = n = 48

Z/2 = 1.645

Margin of error = E = Z/2* ( /n)

= 1.645 * (0.31 / 48)

Margin of error = E = 0.07

At 90% confidence interval estimate of the population mean is,

- E < < + E

2.63 - 0.07 < < 2.63 + 0.07

2.56 < < 2.70

(2.56 , 2.70)