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For the total population of a large southern city, mean family income is $34,000, with a standard deviation (for the population) of $5,000. Imagine that your are taking a subsample of 200 city residents. What is the probability that the sample mean exceeds $37,000?

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Answer:

Less than .0001

Step-by-step explanation:

The population and sample mean  family income are the same: $34,000.

The sample standard deviation is given by:

[tex]SD=\frac{\sigma}{\sqrt n}\\SD=\frac{\$5,000}{\sqrt 200}\\SD=\$353.55[/tex]

For any give income, X, the correspondent z-score of the distribution is given by:

[tex]z=\frac{X-M}{SD}[/tex]

For X = $37,000:

[tex]z=\frac{37,000-34,000}{353.55}\\z= 8.485[/tex]

Traditional z-score tables present values up to 3.49 at the 99.98-th percentile. A z-score of 8.485, which is way above the upper represented limit, denotes an almost zero probability that the sample mean exceeds $37,000.

It is fair to say that the probability that the sample mean exceeds $37,000 is less than .0001

The mean income and standard deviation of $34,000 and $5,000, gives

the probability the sample mean exceeds $37,000 is approximately 0.

How can the probability that [tex]\overline{x}[/tex] exceed $37,000 be found?

The given parameters are;

Mean family income = $34,000

The standard deviation = $5,000

The sample size = 200

Required:

The probability that the sample mean exceeds $37,000

Solution:

The z-score is found as follows;

[tex]z = \dfrac{37,000 - 34,000}{\dfrac{5,000}{\sqrt{200} } } \approx \mathbf{8.485}[/tex]

The value, 8.485 is larger than the largest value on the z-table which is

3.49, such that we have;

  • The probability that the mean is larger than $37,000 is less than 1 - 0.9998 = 0.0002 ≈ 0

Learn more about the z-score table here:

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