Jennie is making popcorn. The recipe calls for 12 cup of butter, 3 tablespoons of kernels, and 1 teaspoon of salt. If she uses 10 tablespoons of kernels, how much butter does she need? Round your answer to the nearest hundredth.
Since the recipe originally calls for 3 tablespoons of kernels, and Jennie uses 10 tablespoons instead, she uses 10/3= <<10/3=3.33>>3.33 times the original amount of corn.
Thus, she needs 12 x 3.33 = <<12*3.33=39.96>>39.96 cups of butter. Answer: \boxed{39.96}.