A hacker is trying to guess someone's password. The hacker knows (somehow) that the password is 4 characters long, and that each character is either a lowercase letter, (a, b, c, etc) or a numerical digit (0, 1, 2, 3, 4, 5, 6, 7, 8, or 9). Assume that the hacker makes random guesses. What is the probability that the hacker guesses the password on his first try?