3a. Make tables of equivalent ratios relating quantities with whole-number measurements, find-missing values in the tables, and plot the pairs of values on the coordinate plane. Use tables to compare ratios.

Let's say a two-year-old goes through 35 diapers in 7 days. The first part of the standard says students should be able to fill in a table using equivalent ratios to find out things like how many diapers the little dude goes through in 5 days, and how many days it takes him to power through 20 diapers. It's easier if we start out by identifying the simplest form of the ratio and work from there to solve for future events and missing values.

From the table, we can plot and connect ordered pairs to create line graphs to predict future events, like a legit fortune-teller (e.g., how many diapers would the little bugger use after 28 days?).

Try using a piece of spaghetti (imaginary or, if it floats your boat, actual) to connect the points; it helps students see calculation errors (straying points) that sometimes happen from tricky inverse operations. For example, if we were calculating days from diapers, we'd divide by 7; but we'd better remember to multiply by 7 when going from diapers to days.