Use this tool to help when iterating to find a solution (guess & check).

Start by entering the target output, then enter values you've tried along with their results. Use the lines to choose your next input guess.

Imagine you're trying to find the interest rate that causes an initial investment of $100 to reach $200 in 4 years.

You guess r = 0.05, but that's too low.

You try r = 0.10, and that's still too low.

You try r = 0.20, and that's too high.

The lines tell you that your next guess should be r = 0.19.

That's solving by iteration!