Fifteen SmartCars Were Randomly Selected and the Highway Mileage of Each

Multiple Choice

Fifteen SmartCars were randomly selected and the highway mileage of each was noted. The analysis yielded a mean of 47 miles per gallon and a standard deviation of 5 miles per gallon.
Which of the following would represent a 90% confidence interval for the average highway
Mileage of all SmartCars?

A) $47 \pm 1.753 \frac { 5 } { \sqrt { 15 } }$

B) $47 \pm 1.761 \frac { 5 } { \sqrt { 15 } }$

C) $47 \pm 1.645 \frac { 5 } { \sqrt { 15 } }$

D) $47 \pm 1.345 \frac { 5 } { \sqrt { 15 } }$