A woman labels the squares of a very large chessboard 1 through 64. On each square k, the woman puts 2^k grains of rice. How many more grains of rice are placed on the 10th square than on the first 9 squares combined?
sum of the first 9 squares: 2^1 + 2^2 + ... + 2^9 = 2^10 - 1
10th square: 2^10