3d. Use ratio reasoning to convert measurement units; manipulate and transform units appropriately when multiplying or dividing quantities.

The last part of this standard asks students to apply ratio reasoning to convert stuff into other stuff, like some kind of math-alchemist. Ratio reasoning is proportional reasoning, which is a little different than setting up proportions to solve. (We'll cover that in seventh grade.) Students should be able to take equivalent units and turn them into conversion factors (i.e., a unit rate that compares the unit you're looking for to the unit you actually have).

For example, 1 kg = 2.2 lbs. If each soiled diaper weighs 1.2 pounds, we can figure out how many kilograms the diaper weighs by multiplying by the conversion factor of . We always multiply by the conversion factor, even when we end up dividing. Students should also recognize how to kick this process into reverse; if they need to covert pounds to kilograms instead, they'd need to use . And if they think this process stinks, just hand them a poopy diaper.