Two Independent Samples of Sizes 30 and 40 Are Randomly $\bar { X } _ { 1 } - \bar { X } _ { 2 }$

question 45

Multiple Choice

Two independent samples of sizes 30 and 40 are randomly selected from two populations to test the difference between the population means, µ?1 - µ?2, where the population variances are unknown but equal. Which of the following best describes the sampling distribution of the sample mean difference $\bar { X } _ { 1 } - \bar { X } _ { 2 }$ ?

• A)Normal.
• B)t-distributed with 68 degrees of freedom.
• C)Approximately normal.
• D)None of these choices are correct.