Respuesta :
Answer:
a) The standard score associated with a gestation period of 13.8 months is of [tex]Z = -1[/tex]
b) 34% of whale pregnancies will have a gestation period between 13.8 and 15 months.
c) Since when [tex]X = 21[/tex], [tex]Z = 5 \geq 2[/tex], it would be unusual for a whale to have a gestation period of 21 months.
Step-by-step explanation:
The Empirical Rule states that, for a normally distributed random variable:
Approximately 68% of the measures are within 1 standard deviation of the mean.
Approximately 95% of the measures are within 2 standard deviations of the mean.
Approximately 99.7% of the measures are within 3 standard deviations of the mean.
Normal Probability Distribution:
Problems of normal distributions can be 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.
If [tex]Z \geq 2[/tex] or [tex]Z \leq -2[/tex], the measure X is considered to be unusual.
According to a website, the mean gestation period for a whale is 15 months. Assume the distribution of gestation periods is Normal with a standard deviation of 1.2 months.
I corrected to 1.2 because it is what makes sense considering the questions.
This means that [tex]\mu = 15, \sigma = 1.2[/tex]
a. Find the standard score associated with a gestation period of 13.8 months
This is Z when X = 13.8. So
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{13.8 - 15}{1.2}[/tex]
[tex]Z = -1[/tex]
The standard score associated with a gestation period of 13.8 months is of [tex]Z = -1[/tex]
b. Using the Empirical Rule and your answer to part a, what percentage of whale pregnancies will have a gestation period between 13.8 and 15 months?
The standard score associated with a gestation period of 13.8 months is of [tex]Z = -1[/tex], which means that it is one standard deviation below the mean.
The normal distribution is symmetric, which means that of the approximately 68% of measures within one standard deviation of the mean, 68%/2 = 34% are within one standard deviation below the mean(in this case, 13.8) and the mean(in this case 15), and 34% are within the mean and one standard deviation above the mean.
So 34% of whale pregnancies will have a gestation period between 13.8 and 15 months.
c. Would it be unusual for a whale to have a gestation period of 21 months? Why or why not?
Let's find the z-score
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{21 - 15}{1.2}[/tex]
[tex]Z = 5[/tex]
Since when [tex]X = 21[/tex], [tex]Z = 5 \geq 2[/tex], it would be unusual for a whale to have a gestation period of 21 months.
