Have you ever wondered why you’d need to be able to convert and understand equivalent units of weight? Why would it matter whether something was calculated from ounces to pounds, or from pound to tons, or from tons to pounds, or from pounds back to ounces? Well, the reason’s as simple as mailing a package with the United States Postal Service!

#### Why It Matters

Since January 2013, when you mail a package, the post office charges $1.95 for the first 3 ounces of weight. Each additional ounce thereafter costs $0.17. You need to understand pounds and ounces if you are planning to mail a package that weighs 2 pounds.

How would you figure out the cost of this 2-pound package? Well, you know that there are 16 ounces in 1 pound. The package weighs 2 pounds, which is equivalent to 32 ounces. Given that the first 3 ounces cost $1.95 and each additional ounce is $0.17, we can figure out the cost for 32 ounces of package:

\begin{align*}\$ 1.95 + \$ 0.17(32-3)= \$ 1.95 + \$ 0.17(29) = \$ 1.95 + \$ 4.93 = \$ 6.88\end{align*}

See how the post office works: http://www.youtube.com/watch?v=KYFtalTNzKk

#### Explore More

Visit the following website to play a variety of interactive measurement games.

http://www.aasd.k12.wi.us/staff/boldtkatherine/MathResources3-6/Math_Measurement.htm