Units of Mass (Pounds and Ounces)
Ximena saw a package of imported meat at a supermarket labeled "5 lb." In Mexico, meat is sold by the kilogram. How many kilograms is that? And how much would it cost? To answer, you need two units from the English system: the pound and the ounce.
Two systems, one mass
In Mexico we measure mass with the International System of Units (SI): grams (g) and kilograms (kg), where $1\text{ kg} = 1{,}000\text{ g}$. In the United States, on the other hand, they use the English system: pounds (lb) and ounces (oz). You will see them on imported product labels, online recipes, and airline rules.
The values you need:
Notice that these equivalences are approximate: a pound does not fit into a gram an exact number of times. That is why results are rounded.
A sack of sugar weighs 10 pounds. How many grams is that? Use $1 \text{ pound} = 453.6 \text{ g}$.
A sack of sugar weighs 10 pounds. How many grams is that? Use $1 \text{ pound} = 453.6 \text{ g}$.
Converting with a conversion factor
A conversion factor is a fraction that equals 1, because the top and bottom are the same amount in different units: $\dfrac{453.6\text{ g}}{1\text{ lb}} = 1$. Multiplying by 1 does not change the mass, it only changes how it is written. You arrange it so that the unit you want to get rid of cancels out.
To go from grams to pounds you do the opposite: you divide by the value of a pound.
A baby weighed 7 pounds at birth. Convert that weight to kilograms. Use $1 \text{ pound} = 0.4536 \text{ kg}$.
A baby weighed 7 pounds at birth. Convert that weight to kilograms. Use $1 \text{ pound} = 0.4536 \text{ kg}$.
A bag of potato chips contains 8 ounces of product. How many grams is that? Use $1 \text{ ounce} = 28.35 \text{ g}$.
A bag of potato chips contains 8 ounces of product. How many grams is that? Use $1 \text{ ounce} = 28.35 \text{ g}$.
Pounds and ounces together
Since $1\text{ lb} = 16\text{ oz}$, you can go from one to the other with the same method. To get from ounces to grams, use $28.35\text{ g}$ per ounce. To go through pounds: $\dfrac{16\text{ oz}}{1\text{ lb}}$.
In the English system $1 \text{ pound} = 16 \text{ ounces}$. A recipe calls for 12 ounces of cheese. How many grams of cheese are needed?
In the English system $1 \text{ pound} = 16 \text{ ounces}$. A recipe calls for 12 ounces of cheese. How many grams of cheese are needed?
Problems in context
First convert, then solve what the problem asks.
A package of hamburger meat says "5 lb". One kilogram of that meat costs $\$180…
A package of hamburger meat says "5 lb". One kilogram of that meat costs $\$180$ at the butcher's. How many kilograms does the package contain, and how much would it cost to buy it in Mexico?
A suitcase can carry a maximum of 50 pounds on a flight. If you are already carrying 18 kg of clothes, how many more kilograms can you add without going over the limit?…
A suitcase can carry a maximum of 50 pounds on a flight. If you are already carrying 18 kg of clothes, how many more kilograms can you add without going over the limit? Use $1 \text{ pound} = 0.4536 \text{ kg}$ and round to one decimal place.
Back to the beginning: Ximena's 5-lb package contains $2.268\text{ kg}$ and would cost $\$408.24$.