You might not think math has much to do with cooking, but the truth is that the better your math skills are, the better you’ll be in the kitchen. Just consider the importance of math while you're trying to follow a recipe.
TL;DR (Too Long; Didn't Read)
Math shows up in many aspects of cooking and baking, including converting temperature from Celsius to Fahrenheit (and vice versa), changing the quantities of ingredients provided by a recipe and working out cooking times based on weight.
Sometimes, a recipe might provide cooking temperatures in Celsius, but the dial on your range displays Fahrenheit, and vice versa. If you know the formula to convert Celsius to Fahrenheit you can easily figure out what to set your dial to. The formula is F = ((9 ÷ 5) x C) + 32. For example, if the Celsius temperature is 200, you convert it to Fahrenheit by working out ((9 ÷ 5) x 200) + 32, i.e. 360 + 32, which is 392 degrees Fahrenheit. To convert a temperature of 392 degrees Fahrenheit to Celsius, the calculation is (392 - 32) ÷ (9 ÷ 5).
If you want to make more than one batch, you need bigger quantities of every ingredient. Multiple each ingredient by the number of batches. For example, if a recipe provides an ingredient list for six cookies but you want to make 12 cookies, you need to multiply all ingredients by two to make your larger batch. That may involve multiplying fractions, for example if the recipe calls for 2/3 cup of milk, and you need to double it, the formula is 2 x 2/3 = 4/3 = 1 and 1/3.
A knowledge of fractions is also useful if you want to make a smaller batch than the recipe. For example, if the recipe provides an ingredient list for 24 cookies, but you only want to make six cookies. In this case, you need to quarter each ingredient. So if the recipe requires two teaspoons of baking powder, you only need 1/2 a teaspoon because 2 ÷ 4 = 1/2.
Weight and Cooking Time
You often have to work out how long to cook something based on its weight, such as a turkey for Thanksgiving dinner. First, you may need to thaw that turkey. If a turkey has to thaw in the refrigerator for 24 hours per 5 pounds, how long do you need to thaw a 10-pound turkey? To work this out, you take the weight of the turkey and multiply it by the time value you already have, i.e. 10 x 24. Next, you divide this figure (240) by 5 pounds. The answer (48) is the number of hours you have to thaw a 10-pound turkey. To work out how long you have to cook something, the formula is cooking time in minutes = 15 + ((mass in grams ÷ 500) x 25). For example, if you have a chicken that weighs 2.8 kg, the calculation is 15 + ((2800 ÷ 500) x 25). The answer is 155 minutes, meaning you have to cook the chicken for 2 hours and 35 minutes.