A metropolitan school system consists of three districts - north, south, and central. The north district contains 25% of all students, the south district contains 40% of all students, and the central district contains 35%. A minimum competency test was given to all students. 10% of the north district students failed, 15% of the south district students failed, and 5% of the central district students failed.
A - develop a probability tree showing all marginal, conditional, and joint probabilities
B - develop a joint probability table.
C - What is the probability that a student selected at random failed the test