1. (5') A random sample of 10 students were asked to indicate the number of hours per week that they surf the net:

{y_i |10,11,8,9,12,9,12,9,10,12}

(a) Calculate the sample size n, sample mean , and standard deviation s.

(b) Assume that the t-statistic follows the t-distribution with the degrees of freedom n-1. Find 95% confidence interval of .

(c) Find the critical value and reject region for the null hypothesis against at the 5% size.

(d) Test the null hypothesis against at the 5% size.