A certain test preparation course is designed to help students improve their scores on the GMAT exam. A mock exam is given at the beginning and end of the course to determine the effectiveness of the course. The following measurements are the net change in 3 students' scores on the exam after completing the course: 17,20,26
Using these data, construct a 95% confidence interval for the average net change in a student's score after completing the course. Assume the population is approximately normal.

Step 4 of 4 : Construct the 95% confidence interval. Round your answer to one decimal place.