A test to determine whether a certain antibody is present is 99.6​% effective. This means that the test will accurately come back negative if the antibody is not present​ (in the test​ subject) 99.6​% of the time. The probability of a test coming back positive when the antibody is not present​ (a false​ positive) is 0.004. Suppose the test is given to four randomly selected people who do not have the antibody.
​(a) What is the probability that the test comes back negative for all four ​people?
​(b) What is the probability that the test comes back positive for at least one of the four ​people?