A sandwich shop is giving away short hoagies to celebrate ten years in business. The first 45 customers can reach into a glass jar and select a sandwich written on a small piece of paper. The papers contain 15 turkey sandwiches, 20 ham sandwiches, and 10 roast beef sandwiches. The customers cannot see which sandwich is written on the paper until after they select it. The first five customers select two turkey sandwiches, two ham sandwiches, and one roast beef sandwich. What is the probability that the sixth customer will pick a roast beef sandwich?

Instructions: Enter your answer as a fraction. Example: a/b