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Scores on a certain exam are normally distributed with a mean of 90 and a variance of 25. What is the score obtained by the top 2.5% of the students?

A. 99.8
B. 86.25
C. 80.2
D. 139.0
E. 85.50

Answer :

Final answer:

The question relates to the concepts of normal distribution and percentiles in statistics. The score obtained by the top 2.5% of students is likely to be 99.8, calculated using the mean, standard deviation, and z-score corresponding to the top 2.5%. This represents the value of test scores that is higher than 97.5% of the scores. The correct answer is option(a).

Explanation:

The subject of the question is based on statistical concepts, specifically normal distribution and percentiles. You have been given that scores on a certain exam are normally distributed with a mean of 90 and a variance of 25. That variance gives a standard deviation of 5, as the variance is the square of the standard deviation.

To find the score obtained by the top 2.5% of the students, you need to refer to the concept of z-score, which tells us how many standard deviations a data point is away from the mean. In this case, you're searching for z corresponding to the top 2.5%, which from standard z-tables is roughly 1.96.

Substituting these values, which are mean (μ = 90), standard deviation (σ = 5), and z-score (1.96) to calculate score (X): X = μ + zσ gives you : X = 90 + (1.96)(5) which approximately equals 99.8. Hence, option a. 99.8 is the likely answer.

Learn more about Normal Distribution here:

https://brainly.com/question/30390016

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