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Using the normal distribution, it is found that the replacement time that separates the top 18% from the bottom 82% is of 11.23 years.
<h3>Normal Probability Distribution</h3>The z-score of a measure X of a normally distributed variable with mean and standard deviation
is given by:
- 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.
In this problem, the mean and the standard deviation are, respectively, given by .
The desired value is the 82nd percentile, which is X when Z = 0.915, hence:
X - 9.4 = 0.915(2)
X = 11.23
The replacement time that separates the top 18% from the bottom 82% is of 11.23 years.
More can be learned about the normal distribution at brainly.com/question/24663213