Imagine that you're in the supermarket comparing a big bag of candy to a small bag of candy. Sure, the small bag of candy costs less – but is it possible the big bag of candy might save you money in the long run? The key to finding out is knowing how to calculate how much each bag of candy costs per pound. Then, it is easy to compare them and find out which bag is the better value. This is a handy example of when math comes alive in the real world. After you master the basic technique, you can apply it to any situation you encounter.
TL;DR (Too Long; Didn't Read)
To calculate the cost of any item per pound, divide the cost of the item by its weight in pounds.
Converting Weight to Pounds
To calculate the cost per pound, you need two things: the cost of the item in question and the weight of the item in question. The weight has to be in pounds, but if the weight isn't given in pounds, you can convert it. Here are two of the common units of measure you might need to convert into pounds, along with how to convert them:
Ounces: Divide by 16 to get the weight in pounds. So, to convert to pounds, you would calculate:
Kilograms: Multiply by 2.2046 to get the weight in pounds. If you have 5 kilograms, that's equal to:
Calculating the Cost Per Pound
When you have the cost of an item and its weight in pounds, you're ready to calculate its cost per pound. All you have to do is divide the total cost of the item by the number of pounds it weighs. So if your big bag of candy weighs 5 pounds and costs $13, you'd divide the cost by the weight in pounds:
An Example Using Ounces
What about the small bag of candy? Let's say it weighs 8 ounces and costs $4. First, convert 8 ounces to pounds. Using the formula given above for ounces:
So the small bag weighs 0.5 pounds. Now that you have the small bag's weight in pounds, you can divide the cost by the weight in pounds:
Finishing the Real World Example
Now that you know how much each bag of candy costs per pound, you can compare them to see which is the better value. Although the small bag of candy costs a lot less than the big bag, it costs a whopping $8 per pound. The big bag is a better value because it costs only $2.60 per pound for the same product.
About the Author
Lisa studied mathematics at the University of Alaska, Anchorage, and spent several years tutoring high school and university students through scary -- but fun! -- math subjects like algebra and calculus.
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