Answer:
D. 0.9938.
Step-by-step explanation:
To solve this question, we need to understand the normal probability distribution and the central limit theorem.
Normal Probability Distribution
Problems of normal distributions can be solved using the z-score formula.
In a set with mean
and standard deviation
, the z-score of a measure X is given by:
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.
Central Limit Theorem
The Central Limit Theorem establishes that, for a normally distributed random variable X, with mean
and standard deviation
, the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean
and standard deviation
.
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
Mean of 115 and a standard deviation of 8.
This means that ![\mu = 115, \sigma = 8](https://tex.z-dn.net/?f=%5Cmu%20%3D%20115%2C%20%5Csigma%20%3D%208)
100 people are randomly selected
This means that ![n = 100, s = \frac{8}{\sqrt{100}} = 0.8](https://tex.z-dn.net/?f=n%20%3D%20100%2C%20s%20%3D%20%5Cfrac%7B8%7D%7B%5Csqrt%7B100%7D%7D%20%3D%200.8)
Find the probability that their mean blood pressure will be less than 117.
This is the p-value of Z when X = 117, so:
![Z = \frac{X - \mu}{\sigma}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7BX%20-%20%5Cmu%7D%7B%5Csigma%7D)
By the Central Limit Theorem
![Z = \frac{X - \mu}{s}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7BX%20-%20%5Cmu%7D%7Bs%7D)
![Z = \frac{117 - 115}{0.8}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7B117%20-%20115%7D%7B0.8%7D)
![Z = 2.5](https://tex.z-dn.net/?f=Z%20%3D%202.5)
has a p-value of 0.9938, and thus, the correct answer is given by option D.