A class of 135 students took a final examination in mathematics. The scores were normally distributed with a mean score of 68% and a standard deviation of 8.5%. Determine the percentile rank of each of the following people: (a) Jennifer, who scored 78 % (b) Steven, who got 55 % (c) Jessica, who was very happy with her mark of 89 %

Zoagliaj

Zoagliaj

Answered question

2022-07-17

A class of 135 students took a final examination in mathematics. The scores were normally distributed with a mean score of 68% and a standard deviation of 8.5%. Determine the percentile rank of each of the following people:
(a) Jennifer, who scored 78 %
(b) Steven, who got 55 %
(c) Jessica, who was very happy with her mark of 89 %

Answer & Explanation

Osvaldo Crosby

Osvaldo Crosby

Beginner2022-07-18Added 12 answers

Given :
n = 135
Mean = μ = 68
Standard deviation = σ = 8.5
a) Z = X μ σ = 78 68 8.5 = 1.18
P(Z < 1.18) = 0.8810 (from standard normal table)
Percentile rank = 88.10%
b) Z = 55 68 8.5 = 1.53 P ( Z < 1.53 ) = 0.0630 Percentile rank = 6.3 %
c) Z = 89 68 8.5 = 2.47 P ( Z < 2.47 ) = 0.9932 Percentile rank = 99.32 %

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