1). In 3 fair coin tosses, what is the probability of obtaining exactly 2 tails? (Note In a fair coin toss the 2 outcomes, heads and tails, are equally likely).

I don't understand why the answer is 3/8??

2). In a shipment of 1000 light bulbs, 1/40 of the bulbs were defective. What is the ratio of defective bulbs to non-defective bulbs?

Why is the answer 1/39??