On a unit test in a statistics class, the teacher determines that the mean test grade was 77 point 5 with a standard deviation of 5 point 2 One test grade has a z -score of 2 point 4 Which of the following statements gives the best interpretation of this z -score?
Answer
A
This student’s test grade was higher than 2 point 4 percent of the other students’ test grades.
B
This student’s test grade was 2 point 4 standard deviations below the mean test grade.
C
This student’s test grade was 2 point 4 standard deviations above the mean test grade.
D
The student’s test grade was lower than 2 point 4 percent of the other students’ test grades.
Explanation
A z-score tells how many standard deviations a value is from the mean. Since the z-score is positive 2.4, this student's test grade was 2.4 standard deviations above the mean grade. Therefore, choice C is correct; a negative z-score would indicate a grade below the mean.
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