A ratio compares quantities; a conversion factor changes units without changing the underlying amount. Label quantities so you know which terms correspond.
Key Rules
For a part-to-part ratio, add the parts before comparing with a total.
Scale all parts of a ratio by the same factor.
In a conversion, arrange each factor so the unwanted unit cancels.
Common Mistakes to Avoid
Treating a part-to-part ratio as a part-to-total fraction.
Multiplying by a conversion factor in the wrong direction.
SAT Strategy Tips
→Keep unit labels in every step.
→Check whether a result should be numerically larger or smaller after changing units.
Example Question
The ratio of red beads to blue beads is 3:5. There are 64 beads in total. How many are blue?
Ready to practice?
Apply what you learned with real SAT questions on this topic.