Three plants, C1, C2 and C3, produce respectively 10, 50 and 40 percent of a company’s output. Although plant C1 is a small plant, its manager believes in high quality and only 1 percent of its products are defective. The other two, C2 and C3, are worse and produce items that are 3 and 4 percent defective, respectively. All products are sent to a central warehouse. One item is selected at random and observed to be defective. Find the conditional probability that it comes from plant C1.