A random sample of 25 round trip flights between Philadelphia and Dallas has an average airfare of 393.50 with a sample Standard Deviation of $50.30. The critical value for an 80% confidence interval around this sample mean

Which of the following are independent events? a) knowing that it is going to rain tomorrow, and bringing an umbrella to schoolb) knowing that you have to get up early tomorrow, and going to bed before 9 p.mc) knowing that it is going to rain tomorrow, and going to bed before 9 p.md) knowing that you have a test in school tomorrow, and studying thw night before