Question

A study of the amount of time it takes a specialist to repair a mobile MRI shows that the mean is 8.4 hours and the standard deviation is 1.8 hours. If 32 broken mobile MRIs are randomly selected, find the probability that their mean repair time is less than 8.9 hours.

Answer 1

Using the normal distribution, it is found that there is a 0.0582 = 5.82% probability that their mean repair time is less than 8.9 hours.

Normal Probability Distribution

The z-score of a measure X of a normally distributed variable with mean $\mu$ and standard deviation $\sigma$ is given by:

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

• The z-score measures how many standard deviations the measure is above or below the mean.

• Looking at the z-score table, the p-value associated with this z-score is found, which is the percentile of X.

• By the Central Limit Theorem, the sampling distribution of sample means of size n has standard deviation $s = \frac{\sigma}{\sqrt{n}}$.

In this problem, the parameters are given as follows:

$\mu = 8.4, \sigma = 1.8, n = 32, s = \frac{1.8}{\sqrt{32}} = 0.3182$

The probability that their mean repair time is less than 8.9 hours is the p-value of Z when X = 8.9, hence:

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

By the Central Limit Theorem

$Z = \frac{X - \mu}{s}$

$Z = \frac{8.9 - 8.4}{0.3182}$

Z = 1.57

Z = 1.57 has a p-value of 0.9418.

1 - 0.9418 = 0.0582.

0.0582 = 5.82% probability that their mean repair time is less than 8.9 hours.

More can be learned about the normal distribution at https://brainly.com/question/27643290

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