Suppose a sample of 20 Americans is selected as part of a study of the state of the nation. The Americans in the sample are asked whether or not they are satisfied with the way things are going in the United States. 

a. Compute the probability that exactly 4 of the 20 Americans surveyed are satisfied with the way things are going in the United States. 

b. Compute the probability that at least 2 of the Americans surveyed are satisfied with the way things are going in the United States. 

c. For the sample of 20 Americans, compute the expected number of Americans who are satisfied with the way things are going in the United States. 

d. For the sample of 20 Americans, compute the variance and standard deviation of the number of Americans who are satisfied with the way things are going in the United States.