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irga5000 [103]
3 years ago
13

The heights of the men age 18 and over in HANES5 averaged 69 inches; the SD was 3 inches. Suppose the histogram of their heights

follows the normal curve. Such a man that is 6 feet tall is at the percentile of this height distribution. (Enter the nearest whole number.) What is the 25th percentile, to the nearest inch
Mathematics
1 answer:
emmasim [6.3K]3 years ago
7 0

Answer:

a) 84th percentile.

b) The 25th percentile is of 67 inches.

Step-by-step explanation:

Normal Probability Distribution:

Problems of normal distributions can be solved using the z-score formula.

In a set with mean \mu and standard deviation \sigma, the z-score 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 p-value, we get the probability that the value of the measure is greater than X.

The heights of the men age 18 and over in HANES5 averaged 69 inches; the SD was 3 inches.

This means that \mu = 69, \sigma = 3

Such a man that is 6 feet tall is at the percentile of this height distribution.

6 feet = 6*12 inches = 72 inches. So this percentile is the p-value of Z when X = 72. So

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

Z = \frac{72 - 69}{3}

Z = 1

Z = 1 has a p-value of 0.84, so 84th percentile.

What is the 25th percentile, to the nearest inch

X when Z has a p-value of 0.25, so X when Z = -0.675.

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

-0.675 = \frac{X - 69}{3}

X - 69 = -0.675*3

X = 67

The 25th percentile is of 67 inches.

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