Answer:
0.227 = 22.7% probability that the mean printing speed of the sample is greater than 18.12 ppm.
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:
![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 p-value, 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.
Mean of 17.42 ppm and a standard deviation of 3.25 ppm.
This means that ![\mu = 17.42, \sigma = 3.25](https://tex.z-dn.net/?f=%5Cmu%20%3D%2017.42%2C%20%5Csigma%20%3D%203.25)
Sample of 12:
This means that ![n = 12, s = \frac{3.25}{\sqrt{12}}](https://tex.z-dn.net/?f=n%20%3D%2012%2C%20s%20%3D%20%5Cfrac%7B3.25%7D%7B%5Csqrt%7B12%7D%7D)
Find the probability that the mean printing speed of the sample is greater than 18.12 ppm.
This is 1 subtracted by the p-value of Z when X = 18.12.
![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{18.12 - 17.42}{\frac{3.25}{\sqrt{12}}}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7B18.12%20-%2017.42%7D%7B%5Cfrac%7B3.25%7D%7B%5Csqrt%7B12%7D%7D%7D)
![Z = 0.75](https://tex.z-dn.net/?f=Z%20%3D%200.75)
has a pvalue of 0.773.
1 - 0.773 = 0.227
0.227 = 22.7% probability that the mean printing speed of the sample is greater than 18.12 ppm.