1.Teachers. A school claims that its teachers have been teaching in the school an average of at least 12.4 years. In a study of 15 teachers, the average time in the school was 11.2 years, and their standard deviation (s) was 2. At ? = 0.10, is the number of years Solution H0:Mean>12.4 H1:Mean<12.4 Z=(X-?)/?/sqrt(n) =(11.2-12.4)/2/sqrt(15)=-2.32 Z for 90% confidence is:1.64 Acceptance region is:(-1.64,+1.64) Since the calculated value is out of region we reject null hypothesis.