Bobby and Joan are playing darts using the board shown below. The radius of the outside circle is 10in., and each of the other circles has a radius 2 in. smaller than the next larger circle. All of the circles have the same center. Bobby has only 1 dart left to throw and needs at least 30 points to win the game. Assuming that his last dart hits at a random point within a single region on the board, what is the percent chance that Bobby will win the game?