Susan wants to throw a party for her mom. She is planning on having 30 guests. For dinner she is making a recipe that makes 2 servings each. Each batch of the recipe calls for 4 potatoes and 1 teaspoon of salt. A potato costs $.10 and a container of salt costs $2 at the supermarket. If each container of salt has 5 teaspoons, how much money will Susan spend on food? Let's think first. Chain of thought:
Susan needs to make 30 / 2 = 15 batches of the recipe. Therefore, she will need 15 * 4 = 60 potatoes. She will also need 1 * 15 = 15 teaspoons of salt. Thus she will have to buy 15 / 5 = 3 containers of salt. Therefore, she will spend 60 * $.1 = $6 on potatoes and 3 * $2 = $6 on salt. Thus, she will spend $6 + $6 = $12 on food.
Therefore, the answer is 12.