View Full Version : right tail p-value: saving on faxing costs w/ 2-day mailing

04-28-2008, 11:58 PM
Hey everyone, thank you in advance for any input :o) I don't think this is right, can anyone help?

Here is the question: Faced with rising fax costs, a firm issued a guideleine that transmissions of 10 pages or more should be sent by 2-day mail instead. Exceptions are allowed, but they want the verage to be 10 or below. The firm examined 35 randomly chosen fax transmissions during the next year, yielding a sample mean of 14.44 with a standard deviation of 4.45 pages.

A) At the .01 level of significance, is the true mean greater than 10?
B) Use Excel to find the right-tail p-value.

The hypothesis test is
Ho: < or equal to 10 vs. H1: > 10

The test statistic
z= (14.44-10)/(4.45/? (35))

The p value= P(Z > z)
p= (Z > 5.902785)

P value is less than significant level, the null hypothesis is rejected and we conclude the alternate hypothesis > 10 is true.

04-29-2008, 08:25 AM
You should use TDIST in Excel.

04-30-2008, 08:46 PM
I do not know how to use Excel for these types of problems, I am still trying to learn. Can anyone tell me if this is correct though? I would really appreciate any input at all.

04-30-2008, 10:05 PM
You are correct on (A). On (B), to get the correct P-value, start by using the HELP function in Excel, and see how the TDIST function is used.

05-01-2008, 10:06 PM
Thanks for confirming A, I will try that in Excel.

05-02-2008, 04:56 PM
sample mean of 14.44 with a standard deviation of 4.45

I believe that royhaas is trying to suggest that you use a t distribution for your calculation rather than a z distribution. The is necessary because you do not know the standard deviation of the population (all faxes); you only know the standard deviation of the sample.