Fifteen castings of a certain type are produced per day in a foundry. The finished castings are inspected and classified as defective or non-defective. Records indicate that of the last 500 castings inspected, 16 were defective. Based on this information, find the following:
(a) The probability of having at no defective castings in a day's production
(b) The probability of having at least two defective castings in a day's production