Proportion Solver
Given a/b = c/x (or any of three knowns), solve for the fourth.
Result
x
12
2/3 = 8/12.
- Equationa/b = c/x
- Cross-multiplya · x = b · c
- Solvedx = (b · c) / a = (3 × 8) / 2
Step-by-step
- Set up the proportion: 2/3 = 8/x.
- Cross-multiply: 2 · x = 3 · 8 = 24.
- Divide by a: x = 24 / 2 = 12.
How to use this calculator
- Enter a, b, and c.
- The calculator solves for x in a/b = c/x.
About this calculator
Two ratios are proportional if a/b = c/d. If three of the four values are known, cross-multiplication solves for the fourth: x = (b · c) / a. This is the foundation of "is the same as" reasoning — recipes scaled by ratio, map distances, mixing dilutions.
Frequently asked
Same logic, swap labels. d = (b · c) / a, just like solving for x.
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