Question

1.) Two students, John and Amy took tests in their classes. John score 85 in his class with average 91 and standard deviation of 5.7. Amy score 71 in her class with average 65 and standard deviation of 12.9. Please compute their respective Z score.

2.) For the following Z scores, please determine their percentiles

(check Z table in the book page 375-378)

Z	Percentile
-1.25
1.25
.63
-.63
0

Answer 1

1.) Two students, John and Amy took tests in their classes. John score 85 in his class with average 91 and standard deviation of 5.7. Amy score 71 in her class with average 65 and standard deviation of 12.9.

Answer : Z score = (Individual Score - mean)/standard deviation

Z score of John = (85 - 91)/5.7 = -1.053

Z score of Amy = (71 - 65)/12.9 = 0.465

(2) Z = -1.25

Percentile = NORMSDIST(-1.25) = 0.1056 or 10.56%

Z = 1.25

Percentile = NORMSDIST(1.25) = 0.8944 or 89.44%

Z = 0.63

Percentile = NORMSDIST(0.63) = 0.7357 or 73.57%

Z = -0.63

Percentile = NORMSDIST(-0.63) = 0.2643 or 26.43%

Z = 0

Percentile = NORMSDIST(0.) = 0.5 or 50%