Population mean In different condition the population mean may results in different way Let us consider two different condition in which population mean have to test. One is when population variance is known and other is when population variance is unknown. When population variance is known, Let Null hypothesis is equal to or less than 20 Alternative hypothesis is greater than 20 The known significance level is .05, Hence, type one error should not exceed .05. We also know that probability of type one error will highest when meu is in breakpoint, Another two test should proceed, One tailed test two tailed test Let us consider, Null hypothesis is equal to 20 Alternative hypothesis not equal to 20 The significance level is equal to .05 One tailed test implies in that situation when critical region place under the one tail, specially right tail shaded area. In contrast with two tail test the critical region places under both tail of the distribution. I