In: Statistics and Probability
A gambler plays a dice game where a pair of fair dice are rolled one time and the sum is recorded. The gambler will continue to place $2 bets that the sum is 6, 7, 8, or 9 until she has won 7 of these bets. That is, each time the dice are rolled, she wins $2 if the sum is 6, 7, 8, or 9 and she loses $2 each time the sum is not 6, 7, 8, or 9 and she keeps playing like this until she's won 7 times.
a. What's the probability she places a total of 12 bets?
b. What's her expected winnings when she stops?