Question: A metropolitan school system consists of three districts south, north, & central. The north district contains 25 percent of all students, the south district contains 40 percent, and the central district contains 35 percent. A minimum-competency test was given to all students; 10 percent of the north district students failed, 15 percent of the south district students failed, and 5 percent of the central district students failed. Find the probability that a student selected at random failed the test?