Problem

Engineers must consider the breadths of male heads when designing helmets. The company researchers have determined that the population of potential clientele have head breadths that are normally distributed with a mean of 7 -in and a standard deviation of 1 -in. Due to financial constraints, the helmets will be designed to fit all men except those with head breadths that are in the smallest $2.9 \%$ or largest $2.9 \%$.

What is the minimum head breadth that will fit the clientele?
\[
\min =
\]

What is the maximum head breadth that will fit the clientele?
\[
\max =
\]

Enter your answer as a number accurate to 1 decimal place.

Answer

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Answer

So, the helmets will be designed to fit men with head breadths between 5.1 inches and 8.9 inches, to one decimal place. The final answer is \(\boxed{[5.1, 8.9]}\)

Steps

Step 1 :First, we need to find the z-scores that correspond to the smallest 2.9% and largest 2.9% of the distribution. In a normal distribution, about 95% of the data falls within two standard deviations of the mean. Therefore, the smallest 2.9% and largest 2.9% correspond to the z-scores that are 2 standard deviations away from the mean.

Step 2 :We can use a z-table or a calculator to find these z-scores. The z-score for the smallest 2.9% is approximately -1.88, and the z-score for the largest 2.9% is approximately 1.88.

Step 3 :Now, we can use these z-scores to find the corresponding head breadths. The formula to convert a z-score to an actual value is: \(X = \mu + Z\sigma\), where \(X\) is the value we're trying to find, \(\mu\) is the mean, \(Z\) is the z-score, and \(\sigma\) is the standard deviation.

Step 4 :For the minimum head breadth: \(\text{min} = \mu + Z\sigma = 7 - 1.88*1 = 5.12 \text{ inches}\)

Step 5 :For the maximum head breadth: \(\text{max} = \mu + Z\sigma = 7 + 1.88*1 = 8.88 \text{ inches}\)

Step 6 :So, the helmets will be designed to fit men with head breadths between 5.1 inches and 8.9 inches, to one decimal place. The final answer is \(\boxed{[5.1, 8.9]}\)

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