2 Two stores sell a certain product Store A has 36 of the sa

2) Two stores sell a certain product. Store A has 36% of the sales, 2% of which are of defective items, and store B has 64% of the sales, 1% of which are of defective items. The difference in defective rates is due to different levels of pre-sale checking of the product. A person receives one of this product as a gift. What is the probability it is defective?

a) 0.014    b) 0.38    c) 0.007    d) 0.015

Solution

defective from A: 2% of 36% = 0.72%
defective from B: 1% of 64% = 0.64%
P(from B given defective) = 0.64 / (0.72 + 0.64) = 0.4705

(b) 0.38