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The manager of a computer retails store is concerned that his suppliers have been giving him laptop computers with lower than average quality. His research shows that replacement times for the model laptop of concern are normally distributed with a mean of 4.2 years and a standard deviation of 0.6 years. He then randomly selects records on 38 laptops sold in the past and finds that the mean replacement time is 3.9 years. Assuming that the laptop replacement times have a mean of 4.2 years and a standard deviation of 0.6 years, find the probability that 38 randomly selected laptops will have a mean replacement time of 3.9 years or less.

Answers

Answer 1

Answer:

Answer: 0.0010

Step-by-step explanation:

Given the following :

Population Mean(m) = 4.2 years

Sample mean (s) = 3.9

Standard deviation (sd) = 0.6

Number of samples (n) = 38

Calculate the test statistic (z) :

(sample mean - population mean) / (sd / √n)

Z = (3.9 - 4.2) / (0.6 / √38)

Z = (- 0.3) / (0.6 / 6.1644140)

Z = -0.3 / 0.0973328

Z = - 3.0822086

Z = - 3.08

From the z table :

P(Z ≤ - 3.08) = 0.0010

Answer 2

Answer:

Final answer:

The probability that the mean replacement time of a random sample of 38 laptops is 3.9 years or less, assuming the true mean replacement time is 4.2 years, is approximately 0.0038 or 0.38%

Explanation:

To solve this problem, we will use the formula for the Z score of a sample mean:
Z = (x - µ) / (σ/ √n)

In this case, the mean µ is 4.2 years, the standard deviation σ is 0.6 years, the sample mean x is 3.9 years, and the sample size n is 38.

Substituting the given values into the formula, we get:
Z = (3.9 - 4.2) / (0.6/√38) = -2.67.

We can then look up this Z score in the Z score table or use statistical software to find the corresponding probability. The probability associated with Z = -2.67 is approximately 0.0038. This means there's about a 0.38% chance that the mean replacement time of a random sample of 38 laptops will be 3.9 years or less, assuming the true mean replacement time is 4.2 years.

Learn more about Probability here:

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