8.4.5 Suppose that the fluctuations in the price of a share of stock in a certain company are well described by a geometric Brownian motion with drift D ????0:1 and variance 2 D 4. A speculator buys a share of this stock at a price of $100 and will sell if ever the price rises to $110 (a profit) or drops to $95 (a loss). What is the probability that the speculator sells at a profit?