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Natasha2012 [34]
3 years ago
7

The average high-school teacher annual salary is $43,000. Let teacher salary be normally distributed with a standard deviation o

f $18,000.a. What percent of high school teachers make between $40,000 and $50,000? Round to 3 decimals and keep '0' before the decimal point.b. What percent of high school teachers make more than $80,000? Round to 3 decimals and keep '0' before the decimal point.
Mathematics
1 answer:
Dvinal [7]3 years ago
6 0

Answer:

a) 0.219

b) 0.02

Step-by-step 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 = \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 = 43000, \sigma = 18000

a. What percent of high school teachers make between $40,000 and $50,000?

This is the pvalue of Z when X = 50,000 subtracted by the pvalue of Z when X = 40,000.

So

X = 50,000

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

Z = \frac{50000 - 43000}{18000}

Z = 0.39

Z = 0.39 has a pvalue of 0.6517.

X = 40,000

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

Z = \frac{40000 - 43000}{18000}

Z = -0.17

Z = -0.17 has a pvalue of 0.4325

So 0.6517 - 0.4325 = 0.219 = 21.9% of high school teachers make between $40,000 and $50,000.

b. What percent of high school teachers make more than $80,000?

This is 1 subtracted by the pvalue of Z when X = 80000. SO

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

Z = \frac{80000 - 43000}{18000}

Z = 2.06

Z = 2.06 has a pvalue of 0.9803.

So 1-0.9803 = 0.0197 = 0.02 = 2% of high school teachers make more than $80,000.

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