Question

Suppose that the sitting​ back-to-knee length for a group of adults has a normal distribution with a mean of mu equals 24.4 in. and a standard deviation of sigma equals 1.2 in. These data are often used in the design of different​ seats, including aircraft​ seats, train​ seats, theater​ seats, and classroom seats. Instead of using 0.05 for identifying significant​ values, use the criteria that a value x is significantly high if​ P(x or ​greater)less than or equals0.01 and a value is significantly low if​ P(x or ​less)less than or equals0.01. Find the​ back-to-knee lengths separating significant values from those that are not significant. Using these​ criteria, is a​ back-to-knee length of 26.6 in. significantly​ high?

Answer 1

Answer:

$P(X \geq 26.6) = 0.0336$, which is greater than 0.01. So a back-to-knee length of 26.6 in. is not significantly high.

Step-by-step explanation:

Problems of normally distributed samples are solved using the z-score formula.

In a set with mean $\mu$ and standard deviation $\sigma$, the zscore of a measure X is given by:

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

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.

In this problem, we have that:

$\mu = 24.4, \sigma = 1.2$

In this problem, a value x is significantly high if:

$P(X \geq x) = 0.01$

Using these​ criteria, is a​ back-to-knee length of 26.6 in. significantly​ high?

We have to find the probability of the length being 26.6 in or more, which is 1 subtracted by the pvalue of Z when X = 26.6. So

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

$Z = \frac{26.6 - 24.4}{1.2}$

$Z = 1.83$

$Z = 1.83$ has a pvalue of 0.9664.

1 - 0.9664 = 0.0336

$P(X \geq 26.6) = 0.0336$, which is greater than 0.01. So a back-to-knee length of 26.6 in. is not significantly high.