cowgirl3
Feb 25, 2011, 08:39 PM
I am looking for some help on probabilites of Normal Distributions:
Suppose it is know that the distibution of purchase amounts by customers entering a popular retail store is approximately normal with a mean of $25 and standard deviation of $8.
a)Find the dollar amount such that 75% of all customers spend no more than this amount
b) Find the dollar amount such that 80% of all customers spend at least this amount
c) Find two dollar amounts, equidistant from the mean of $25 such that 90% of all customers purchases are between these values.
I am using the NORMINV function in excel to answer these questions where the first input is probability (x).
My question is for part a, can someone clarify if the probability should be 0.75 or 0.25 (1-.75). I think it should be 0.75
For part b, can someone clarify if the probability should be 0.80 or 0.20 (1-.80). I think it should be 0.20
I am confused between the wording of "Spend no more than" and "spend at least" for part a and b.
For part c, I am not quite sure what I should be doing.
Any help would be appreciated.
Thanks!
Suppose it is know that the distibution of purchase amounts by customers entering a popular retail store is approximately normal with a mean of $25 and standard deviation of $8.
a)Find the dollar amount such that 75% of all customers spend no more than this amount
b) Find the dollar amount such that 80% of all customers spend at least this amount
c) Find two dollar amounts, equidistant from the mean of $25 such that 90% of all customers purchases are between these values.
I am using the NORMINV function in excel to answer these questions where the first input is probability (x).
My question is for part a, can someone clarify if the probability should be 0.75 or 0.25 (1-.75). I think it should be 0.75
For part b, can someone clarify if the probability should be 0.80 or 0.20 (1-.80). I think it should be 0.20
I am confused between the wording of "Spend no more than" and "spend at least" for part a and b.
For part c, I am not quite sure what I should be doing.
Any help would be appreciated.
Thanks!