Step 1 :Define the probabilities: the probability that a car requires an oil change is 0.71, the probability that a car requires brake repair is 0.29, and the probability that a car requires both an oil change and brake repair is 0.11.
Step 2 :Calculate the probability of either event happening. This is done by adding the probability of an oil change and the probability of a brake repair, then subtracting the probability of both happening. This is because the event of both happening has been counted twice - once in the oil change probability and once in the brake repair probability.
Step 3 :Using the formula \(P(A \cup B) = P(A) + P(B) - P(A \cap B)\), where \(P(A)\) is the probability of an oil change, \(P(B)\) is the probability of a brake repair, and \(P(A \cap B)\) is the probability of both an oil change and brake repair, we find that the probability of either event is \(0.71 + 0.29 - 0.11 = 0.89\).
Step 4 :Final Answer: The probability that the car requires an oil change or brake repair is \(\boxed{0.89}\).