Frank is making salad dressing for a large party. If a serving is 2 1/2 tablespoons, how many servings can he make with 85 tablespoons?

To determine how many servings Frank can make with 85 tablespoons, you need to divide the total amount of tablespoons Frank has by the amount of tablespoons in a serving.

85 tablespoons / 2 1/2 tablespoons = <<85/2.5=34>>34 servings.
Therefore, Frank can make 34 servings of salad dressing. Answer: \boxed{34}.