SOLUTION: The final exam scores of students taking a biology course at a university are normally distributed with a population mean of 73 and population standard deviation of 15. Nine studen

Question 361608: The final exam scores of students taking a biology course at a university are normally distributed with a population mean of 73 and population standard deviation of 15. Nine students are randomly selected from the university and let x be their average score.
What is the probability that their average biology score x is between 60 and 80?

Here's what I have so far...
z=(60-73)/5, z=(80-73)/5
z=-2.6;1.4
P(-2.6 < x < 1.4)
P(z<1.4)-P(z<-2.6)
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
The final exam scores of students taking a biology course at a university are normally distributed with a population mean of 73 and population standard deviation of 15. Nine students are randomly selected from the university and let x be their average score.
What is the probability that their average biology score x is between 60 and 80?
Here's what I have so far...
z=(60-73)/5,e z=(80-73)/5
z=-2.6;1.4
P(-2.6 < x < 1.4)
P(z<1.4)-P(z<-2.6)
----------------------
You say the standard deviation is 15,
but you use 5 as the standard deviation.
----
Assuming 5 is the correct number, you
z-values are correct.
----
Your conclusion should be the following:
P(60 < x < 80) = P(-2.6 < z < 1.4) = 0.9146
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Cheers,
Stan H.
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