To find out how many servings Frank can make with 85 tablespoons when each serving is 2 1/2 tablespoons, you can divide the total number of tablespoons by the number of tablespoons per serving.
First, convert 2 1/2 tablespoons to an improper fraction:
2 1/2 = 2 + 1/2 = 2*2/2 + 1/2 = 4/2 + 1/2 = 5/2 tablespoons.
Now, divide 85 tablespoons by 5/2 servings:
\[ 85 \div \left(\frac{5}{2}\right) = 85 \times \left(\frac{2}{5}\right) = \frac{85 \times 2}{5} = \frac{170}{5} = 34. \]
So, Frank can make 34 servings with 85 tablespoons of salad dressing.