Students use multiplication and division to convert quantities from one unit to another. 

Unit conversion requires an understanding of the relationship between two measures.  The phrase "30 miles per gallon" means that for every one gallon, a car can travel 30 miles.

It is expressed mathematically as 30 miles/1 gallon.  If we want to convert gallons to liters, we need to multiply so that the gallon units cancel out.  In this case, multiple 30 miles/1 gallon x 1 gallon/3.785 liters = 7.92 miles per liter.

Students recall common conversion ratios, such as:

• Kilograms in a pound
• Kilometers in a mile
• Relationship between millions, billions and trillions