Respuesta :
Answer:
P(111.2-cm < ¯ x < 111.4-cm) = 0.4726
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 [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the zscore of a measure X is given by:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
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 [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean [tex]\mu[/tex] and standard deviation [tex]s = \frac{\sigma}{\sqrt{n}}[/tex].
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:
[tex]\mu = 111.4, \sigma = 0.5, n = 23, s = \frac{0.5}{\sqrt{23}} = 0.1043[/tex]
Find the probability that the average length of a randomly selected bundle of steel rods is between 111.2-cm and 111.4-cm.
This is the pvalue of Z when X = 111.4 subtracted by the pvalue of Z when X = 111.2. So
X = 111.4
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
By the Central Limit Theorem
[tex]Z = \frac{X - \mu}{s}[/tex]
[tex]Z = \frac{111.4 - 111.4}{0.1043}[/tex]
[tex]Z = 0[/tex]
[tex]Z = 0[/tex] has a pvalue of 0.5.
X = 111.2
[tex]Z = \frac{X - \mu}{s}[/tex]
[tex]Z = \frac{111.2 - 111.4}{0.1043}[/tex]
[tex]Z = -1.92[/tex]
[tex]Z = -1.92[/tex] has a pvalue of 0.0274.
0.5 - 0.0274 = 0.4726
P(111.2-cm < ¯ x < 111.4-cm) = 0.4726
