If I’m in the store and want to know the price-per-pound of food, do I divide the weight by the dollars, or do I divide the dollars by the weight?
In: Economics
You divide the dollars by the weight.
You can actually get that answer from the question: “price per pound”… you’re dividing the price by the number of pounds. If you divide the other way, you’re getting the “pounds per price”, or how many pounds (or fractions of a pound) one dollar will buy.
This is a simple dimensional analysis. The answer is in your question.
Unit of the price is $
The unit of weight is lb (pounds)
per is a division
So the unit of price-per-pound = $/lb This is the unit of the result just do the calculation with the units
If the cost is 10$ and the weight is 2 lb there is only one operation that results in $/lb = price per pound
10$ / 2lb = 5$/lb
the answer is in your question price-per-pound =price/pound
So ” **I divide the dollars by the weight” is correct.**
That is how all units like that work,
mpg= miles per gallon
you drove 100 miles and used 2 gallons of fuel
100miles/ 2 gallon = 50miles/gallon
Do calculation including units is a very simple way to pick up a lot of error as you tend to know the unit of the result you like and can check if that’s what you got.
Think of the “per” as the slash in division.
Price per pound –> price/pound –> $5.60/2lbs –> $2.80/lb
Also, side tip, it can be easier to check the price per ounce in many cases.
There’s a handy trick for this – any time that you say “per X,” it means that X is the thing you’re dividing by. Same order as you’d say it in. So price per pound, you’ll want to divide the price by the number of pounds. Miles per gallon, you divide the miles traveled by the gallons used, and so on.
So if you spend $25 on 10 pounds of chicken, you’d divide 25/10 and get $2.5 per pound.
Divide the dollars by the weight. You are splitting (dividing) the total of the dollars into equal amounts for each pound – so that is the number you want to split up, so that is the number you divide by the other number.
When you say the word “per” picture a “/“ sign. Price/pound of food. It’s dollars by weight.
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