. Slot machines are now video games, with winning determined by electronic random number generators. In the old days, slot machines worked like this: you pull the lever to spin three wheels; each wheel has 20 symbols, all equally likely to show when the wheel stops spinning; the three wheels are independent of each other. Suppose that the middle wheel has 9 bells among its 20 symbols, and the left and right wheels have 1 bell each.
(a) You win the jackpot if all three wheels show bells. What is the probability of winning the jackpot?
(b) What is the probability that the wheels stop with exactly 2 bells showing?