“This page presents an idea for exploring practical algebraic problems without using symbolic variables. I call this tool a “scrubbing calculator”, because you solve problems by interactively scrubbing over numbers until you’re happy with the results.
Background: This work assumes a Soulver-like environment for interactive arithmetic, and picks up where Soulver leaves off. If you haven’t seen Soulver, go see it. You’ll be glad you did.”

http://worrydream.com/#!/ScrubbingCalculator