Justin is interested in buying a digital phone He visited 18

Justin is interested in buying a digital phone. He visited 18 stores at random and recorded the price of the particular phone he wants. The sample of prices had a mean of 153.57 and a standard deviation of 28.91. (a) What t-score should be used for a 95% confidence interval for the mean, , of the distribution? t* = (b) Calculate a 95% confidence interval for the mean price of this model of digital phone: (Enter the smaller value in the left answer box.) to

Solution

a)

alpha = 1 - 0.95 = 0.05

alpha/2 = 0.025

df= 18 -1 =17

t value =2.110

b)

I : 153.57 +/- 2.110 * 28.91 / srqt (18)

I : 153.57 +/- 14.378

I : 139.192 , 167.948