Well, the probability that he gets the first letter right is 1 in 10. There's 10 digits there. Probability that he gets the second letter right is 1 in 10. These are all independent. And probability he gets the letter right, there's 26 equally likely letters that might be in the actual one. So he has a 1 in 26 chance of that one as well. So the probability of the grand prize is 1 in 2,600.