PSY 305 Assignment 1 solution correct answer key 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)?