Answer:
a)
And we can find this probability using the normal standard table or excel and we got:
b)
And we can find this probability with this difference:
And in order to find these probabilities we can use tables for the normal standard distribution, excel or a calculator.
c)
And we can find this probability using the complement rule and the normal standard table or excel and we got:
d)
If a value is lower than 8.9 or higher than 33.7 would be considered as unusual.
Step-by-step explanation:
Previous concepts
Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".
The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".
Part a
Let X the random variable that represent the scores of a population, and for this case we know the distribution for X is given by:
Where and
We are interested on this probability
And the best way to solve this problem is using the normal standard distribution and the z score given by:
If we apply this formula to our probability we got this:
And we can find this probability using the normal standard table or excel and we got:
Part b
And we can find this probability with this difference:
And in order to find these probabilities we can use tables for the normal standard distribution, excel or a calculator.
Part c
And we can find this probability using the complement rule and the normal standard table or excel and we got:
Part d
For this case we can use the rule of thumb that we expect about 95% of the data values between two deviations and we can find the normal limits like this:
If a value is lower than 8.9 or higher than 33.7 would be considered as unusual.