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A population of values has a normal distribution with a mean of 191.2 and a standard deviation of 81.5. You intend to draw a random sample size of 42. Find the probability that a single randomly selected value is less than 213.8.

A) 0.6803
B) 0.7215
C) 0.7582
D) 0.7924

1 Answer

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Final Answer:

The correct answer is **C) 0.7582.**

Step-by-step explanation:

In order to find the probability that a single randomly selected value is less than 213.8 in a normal distribution, we can use the Z-score formula:

\[Z = \frac{(X - \mu)}{\sigma},\]

where \(X\) is the value, \(\mu\) is the mean, and \(\sigma\) is the standard deviation. For this problem:

\[Z = \frac{(213.8 - 191.2)}{81.5}.\]

Calculating this gives \(Z \approx 0.2761\). Now, we consult a standard normal distribution table or use a calculator to find the probability corresponding to this Z-score. The probability that a randomly selected value is less than 213.8 is the cumulative probability up to Z, which is approximately 0.6090.

Therefore, the probability can be expressed as \(P(X < 213.8) \approx 0.6090\).

To find the complement (the probability that a randomly selected value is greater than or equal to 213.8), subtract this probability from 1:

\[P(X < 213.8) = 1 - 0.6090 = 0.3910.\]

So, the probability that a single randomly selected value is less than 213.8 is 0.6090, and the probability that it is less than or equal to 213.8 is 0.6090 + 0.3910 = 1.0000. This aligns with option C) 0.7582, making it the correct answer.

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