Question

Suppose that the scores of a history test are normally distributed with a mean of 565 and a standard deviation of 113. a) What percentage of the scores are less than 450?

Answer 1

Answer:

15.39% of the scores are less than 450

Step-by-step explanation:

Problems of normally distributed samples are 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:

$Z = \frac{X - \mu}{\sigma}$

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:

$\mu = 565, \sigma = 113$

What percentage of the scores are less than 450?

This is the pvalue of Z when X = 450. So

$Z = \frac{X - \mu}{\sigma}$

$Z = \frac{450 - 565}{113}$

$Z = -1.02$

$Z = -1.02$ has a pvalue of 0.1539

15.39% of the scores are less than 450