Answer:
58.32% probability that a randomly selected application will report a GMAT score of less than 600
93.51% probability that a sample of 50 randomly selected applications will report an average GMAT score of less than 600
98.38% probability that a sample of 100 randomly selected applications will report an average GMAT score of less than 600
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 normally distributed samples are solved using the z-score formula.
In a set with mean
and standard deviation
, the zscore of a measure X is given by:
![Z = \frac{X - \mu}{\sigma}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7BX%20-%20%5Cmu%7D%7B%5Csigma%7D)
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.
Central Limit Theorem
The Central Limit Theorem estabilishes 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.
In this problem, we have that:
![\mu = 591, \sigma = 42](https://tex.z-dn.net/?f=%5Cmu%20%3D%20591%2C%20%5Csigma%20%3D%2042)
What is the probability that a randomly selected application will report a GMAT score of less than 600?
This is the pvalue of Z when X = 600. 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)
![Z = \frac{600 - 591}{42}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7B600%20-%20591%7D%7B42%7D)
![Z = 0.21](https://tex.z-dn.net/?f=Z%20%3D%200.21)
has a pvalue of 0.5832
58.32% probability that a randomly selected application will report a GMAT score of less than 600
What is the probability that a sample of 50 randomly selected applications will report an average GMAT score of less than 600?
Now we have ![n = 50, s = \frac{42}{\sqrt{50}} = 5.94](https://tex.z-dn.net/?f=n%20%3D%2050%2C%20s%20%3D%20%5Cfrac%7B42%7D%7B%5Csqrt%7B50%7D%7D%20%3D%205.94)
This is the pvalue of Z when X = 600. So
![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{600 - 591}{5.94}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7B600%20-%20591%7D%7B5.94%7D)
![Z = 1.515](https://tex.z-dn.net/?f=Z%20%3D%201.515)
has a pvalue of 0.9351
93.51% probability that a sample of 50 randomly selected applications will report an average GMAT score of less than 600
What is the probability that a sample of 100 randomly selected applications will report an average GMAT score of less than 600?
Now we have ![n = 50, s = \frac{42}{\sqrt{100}} = 4.2](https://tex.z-dn.net/?f=n%20%3D%2050%2C%20s%20%3D%20%5Cfrac%7B42%7D%7B%5Csqrt%7B100%7D%7D%20%3D%204.2)
![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{600 - 591}{4.2}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7B600%20-%20591%7D%7B4.2%7D)
![Z = 2.14](https://tex.z-dn.net/?f=Z%20%3D%202.14)
has a pvalue of 0.9838
98.38% probability that a sample of 100 randomly selected applications will report an average GMAT score of less than 600