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A set of data values is normally distributed with a mean of 90 and a standard deviation of 4. Give the standard score and approximate percentile for a data value of 89.

User Schylar
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Answer:

Standard score of -0.25.

A data value of 89 is approximately in the 40th percentile.

Explanation:

Problems of normally distributed samples can be solved using the z-score formula.

In a set with mean
\mu and standard deviation
\sigma, the zscore of a measure X is given by:


Z = (X - \mu)/(\sigma)

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.

In this problem, we have that:


\mu = 90, \sigma = 4

Give the standard score and approximate percentile for a data value of 89.

Z when X = 89


Z = (X - \mu)/(\sigma)


Z = (89 - 90)/(4)


Z = -0.25


Z = -0.25 has a pvalue of 0.4013.

So a data value of 89 is approximately in the 40th percentile.

User Shashank Mishra
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