What to do first
List knowns and unknowns. Check whether the problem wants a number, a relationship, or a graph. Solving Equations is the reference lesson.
Read the question
Wrong answers often come from answering a different question than the one asked—especially “how many” versus “how much is left.”
Total and parts
You know a total and one part; you need the other part. Subtract the known part from the total, or write total = part₁ + part₂ and fill in what you know.
Sense-check
Core lesson
Go deeper: Solving Equations. Use the calculators below with your own loan or bill numbers, not only the examples on this page.
Use the calculator
FAQ
- Where is the main lesson?
Solving Equations has the full topic, examples, and practice links.
- Which calculator first?
After your setup is on paper, open Linear & quadratic equation for a quick numeric pass.