psy 305 rsearch stratergy Academic Help

I don’t understand this Psychology question and need help to study.

PSY 305 Assignment 1

1.A professor has been teaching statistics for many years.His records show that the overall mean for final exam scores is 85 with a standard deviation of 10.He believes that this year’s class is superb to the previous classes.The mean for the 40 students is 90.

• What is the null hypothesis?
• What is the research hypothesis?
• Is this a one or two tailed hypothesis?
• Which test should you use? Why?
• Calculate the appropriate statistical test.
• What is the critical value for α = .05?
• What do you conclude?

2. A researcher gives a group of participants (n = 15) a memory technique to use.He finds that they remember on average 20 words (sample standard deviation = 3) while the average number of words remembered in the population is 15.

• What is the null hypothesis?
• What is the research hypothesis?
• Is this a one or two tailed hypothesis?
• Which test should you use?Why?
• Calculate the appropriate statistical test.
• What is the critical value for α = .05?
• What do you conclude?

3.What is the difference between a z-test and a t-test (i.e., when would you use each one)