Thanks, Vinux. Unfortunately, I don't know how to get the critical values for a two-tailed test, either.

Here's the specific example I'm working on:

A sample of 20 customers bought books. x (bar) = $315.40, s = $43.20.

H0: the population mean <= $300 at 0.10 level of significance

(then also at 0.05 level of significance)

Thanks again for any help!

Here the test statistic is

xbar = $315.40, s = $43.20 n = 20 u0 = 300

and the hypothesis is

H0: the population mean <= $300 Vs H1:he population mean > $300

so t = (315-300)/(43.20/20) =6.9444

and for alpha= 0.10 and df 20-1 =19

talpha = 1.32778

**( Use table. If the table is for two sided, then take alpha =0.20. )**
this we will get using excel, use this function TINV(0.2,19) ( since this gives the two sided )

and for alpha =0.05 talpha =1.73

Both the cases t > talpha.

So we reject the hypothesis.

Rgds

VinuX