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Sagot :
Answer:
0.0418 = 4.18% probability that the average income level in the neighborhoods was less than $38,000.
Step-by-step explanation:
To solve this question, we need to understand the normal probability distribution and the central limit theorem.
Normal Probability Distribution:
Problems of normal distributions can be solved using the z-score formula.
In a set with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the zscore of a measure X is given by:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
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.
Central Limit Theorem
The Central Limit Theorem estabilishes that, for a normally distributed random variable X, with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean [tex]\mu[/tex] and standard deviation [tex]s = \frac{\sigma}{\sqrt{n}}[/tex].
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
Jean knows that the mean income level in the country is $40,000, with a standard deviation of $2,000.
This means that [tex]\mu = 40000, \sigma = 2000[/tex]
Jean selected three neighborhoods and determined the average income level.
This means that [tex]n = 3, s = \frac{2000}{\sqrt{3}} = 1154.7[/tex]
What is the probability that the average income level in the neighborhoods was less than $38,000
This is the pvalue of Z when X = 38000. So
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
By the Central Limit Theorem
[tex]Z = \frac{X - \mu}{s}[/tex]
[tex]Z = \frac{38000 - 40000}{1154.7}[/tex]
[tex]Z = -1.73[/tex]
[tex]Z = -1.73[/tex] has a pvalue of 0.0418
0.0418 = 4.18% probability that the average income level in the neighborhoods was less than $38,000.
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