Following are 21 readings taken in August 1989, Is there strong evidence that the average ozone level exceeds 48? 69,70,40,35,59,40,82,48,49,35,60,59,55,46,78,77,49,60,37,38,56 Solution Ho: mu=48 Ha: mu>48 The test statistic is t=(xbar-mu)/(s/vn) =(54.38095-48)/(14.66791/sqrt(21)) =1.99 Assume a=0.05, the critical value is t(0.05, df=n-1=20) =1.72 (from student t table) Since t=1.99 is larger than 1.72, we reject Ho. So we can conclude that the average ozone level exceeds 48.