Water well depths are normally distributed with a mean of 225 m and a standard deviation of 70 m. What is the probability that a single randomly selected well is: (a) less than 120 m deep? (b) between 100 m and 200 m deep?

Researchers were interested in whether relaxation training decreases the number of headaches a person experiences. they randomly assigned 20 participants to a control group or a relaxation training group and noted the change in number of headaches each group reported from the week before training to the week after training. which statistical analysis should be performed to answer the researchers' question?