The rates of on-time flights for commercial jets are continuously tracked by the u. s. department of transportation. recently, southwest air had the best reate with 80 % of its flights arriving on time. a test is conducted by randomly selecting 12 southwest flights and observing whether they arrive on time. (a) find the probability that exactly 4 flights arrive on time. (b) would it be unusual for southwest to have 9 flights arrive on time?