According to the American Red Cross, 7% of people in the United States have blood type O-negative. A simple random sample of size 4 is obtained, and the number of people X with blood type O-negative is recorded. Construct a probability distribution for the random variable X.

Approach This is a binomial experiment with n = 4 trials. We define a success as selecting an individual with blood type O-negative. The probability of success, p, is 0.07, and X is the random variable representing the number of successes with x = 0, 1, 2, 3, or 4.

Step 1 Construct a tree diagram listing the various outcomes of the experiment by listing each outcome as S (success) or F (failure).

Step 2 Compute the probabilities for each value of the random variable X.

Step 3 Construct the probability distribution.