Respuesta :
Answer:
a) 8.23% probability that a piece of pottery will be finished within 95 minutes
b) 0.28% probability that it will take longer than 110 minutes.
Step-by-step explanation:
Normal distribution:
When the distribution is normal, we use 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.
Two variables:
Means [tex]\mu_{a}, \mu_{b}[/tex]
Standard deviations [tex]\sigma_{a}, \sigma_{b}[/tex]
Sum:
[tex]\mu = \mu_{a} + \mu_{b}[/tex]
[tex]\sigma = \sqrt{\sigma_{a}^{2} + \sigma_{b}^{2}}[/tex]
In this question:
[tex]\mu_{a} = 40, \mu_{b} = 60, \sigma_{a} = 2, \sigma_{b} = 3[/tex]
So
[tex]\mu = \mu_{a} + \mu_{b} = 40 + 60 = 100[/tex]
[tex]\sigma = \sqrt{\sigma_{a}^{2} + \sigma_{b}^{2}} = \sqrt{4 + 9} = 3.61[/tex]
A) What is the probability that a piece of pottery will befinished within 95 minutes?
This is the pvalue of Z when X = 95.
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{95 - 100}{3.61}[/tex]
[tex]Z = -1.39[/tex]
[tex]Z = -1.39[/tex] has a pvalue of 0.0823
8.23% probability that a piece of pottery will befinished within 95 minutes.
B) What is the probability that it will take longer than 110 minutes?
This is 1 subtracted by the pvalue of Z when X = 110.
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{110 - 100}{3.61}[/tex]
[tex]Z = 2.77[/tex]
[tex]Z = 2.77[/tex] has a pvalue of 0.9972
1 - 0.9972 = 0.0028
0.28% probability that it will take longer than 110 minutes.
