Computer shop sells three different brands of computers. Of its computers, 25% of brand 1's computers require warranty repair, 30% of brand 2's computers require warranty repair, and 10% of brand 3's computers require warranty repair. Each manufacturer offers a warranty on their computers. What is the probability that a randomly selected purchaser has a computer that will need repair while under warranty? If a customer returns to the store with a computer that needs warranty repair work, what is the probability that it is a brand 1 computer?