Aslice of pizza contains 29 g of carbohydrate, 13 g of protein and an unknown amount of fat. if the pizza contains 280 kcal, how many grams of fat are present? report the answer to 2 significant figures.

When different macronutrients (e.g., carbohydrates) are metabolized, they yield different amounts of energy, commonly measured in kilocalories.

They are given by the following conversion factors:

carbohydrates = 4 kcal/g
protein = 4 kcal/g
fat = 9 kcal/g

If the slice of pizza contains 29 g carbohydrates, that means there are 4 kcal/g × 29 g = 116 kcal from carbohydrates. It contains 13 g protein, so there are 4 kcal/g × 13 g = 52 kcal from protein.

The total number of kilocalories is 280, of which we have accounted for 168 (116+52). 280–168=112 kcal.

So, there are 112 kcal from fat. Using our conversion factor, 112 kcal × 1 g/9 kcal = 12 g fat.