No, I don't mean the kinds of relationships you have with family or friends, I'm talking about ratios and proportions.
A ratio is a relationship between two things. Given a ratio and one
“real world” number, you can always set up a proportion to solve for the
other missing “real world” number. Sometimes you will need to do this
for similar triangles in geometry and sometimes in algebraic word
problems.
Know the difference between values, ratios, and percents. The SAT test-makers value being able to move easily between percents, fractions, and decimals.