A certain test preparation course is designed to help students improve their scores on the LSAT. A mock assingment is g

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A certain test preparation course is designed to help students
improve their scores on the LSAT. A mock assingment 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 assignment after
completing the course:
24,18,11
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 3 of 4:
Find the critical value that should be used in constructing the
confidence interval. Round your answer to three decimal places.