Items Used in Production Process in a Factory Come from Three

Multiple Choice

Items used in production process in a factory come from three suppliers S1, S2 and S3. S1 provides 20%, S2 provides 30% and S3 provides 50%. However, S1 produces 5% (0.05) defective items, S2 produces 2% (0.02) while S3 produces 1% (0.01) . If an item sampled at random was found to be defective, what is the prior probability it came from Supplier S1?

A) 20%.
B) 5%.
C) 2%.
D) 1%.