160 CHAPTER 3 Probability Using the Addition Rule to Find Probabilities A blood bank catalogs the types of blood, including whether it is Rh-positive or Rh-negative, given by donors during the last five days. The number of donors who gave each blood type is shown in the table. 1. Find the probability that a donor selected at random has type O or type A blood. 2. Find the probability that a donor selected at random has type B blood or is Rh-negative. Blood type O A B AB Total Rh-factor Positive 156 139 37 12 344 Negative 28 25 8 4 65 Total 184 164 45 16 409 SOLUTION 1. Because a donor cannot have type O blood and type A blood, these events are mutually exclusive. So, using the Addition Rule, the probability that a randomly chosen donor has type O or type A blood is P1type O or type A2 = P1type O2 + P1type A2 = 184 409 + 164 409 = 348 409 ≈ 0.851. 2. Because a donor can have type B blood and be Rh-negative, these events are not mutually exclusive. So, using the Addition Rule, the probability that a randomly chosen donor has type B blood or is Rh-negative is P1type B or Rh@neg2 = P1type B2 + P1Rh@neg2 - P1type B and Rh@neg2 = 45 409 + 65 409 - 8 409 = 102 409 ≈ 0.249. TRY IT YOURSELF 4 1. Find the probability that a donor selected at random has type B or type AB blood. 2. Find the probability that a donor selected at random does not have type O or type A blood. 3. Find the probability that a donor selected at random has type O blood or is Rh-positive. 4. Find the probability that a donor selected at random has type A blood or is Rh-negative. Answer: Page A38 EXAMPLE 4
RkJQdWJsaXNoZXIy NjM5ODQ=