Calculator Input
Use Solve mode for one missing term, Check mode to verify equivalent ratios, and Scale mode to resize a ratio accurately.
Formula Used
| Unknown term | Formula | Use case |
|---|---|---|
| A | A = (B × C) ÷ D | Use when A is missing. |
| B | B = (A × D) ÷ C | Use when B is missing. |
| C | C = (A × D) ÷ B | Use when C is missing. |
| D | D = (B × C) ÷ A | Use when D is missing. |
| Scaled ratio | New terms = Original terms × k | Use when enlarging or shrinking a ratio. |
How to Use This Calculator
- Choose a mode based on your task: solve, check, or scale.
- For Solve mode, fill any three terms and leave one blank.
- For Check mode, enter all four terms to test equivalence.
- For Scale mode, enter A and B, then provide one scaling driver.
- Set your preferred decimal places for cleaner outputs.
- Press Submit to display the result above the form instantly.
- Review the graph, cross products, and summary table.
- Use the CSV or PDF buttons to export the result.
Example Data Table
| Scenario | Known proportion | Action | Result |
|---|---|---|---|
| Basic solve | 3 : 5 = 9 : x | Solve D | x = 15 |
| Recipe scaling | 2 : 3 | Scale by 4 | 8 : 12 |
| Equivalent check | 4 : 6 and 10 : 15 | Check ratios | Equivalent |
| Map ratio | x : 8 = 15 : 20 | Solve A | x = 6 |
| Classroom grouping | 5 : 7 | Target first term 20 | 20 : 28 |
Why Proportions Matter
Proportions appear in geometry, similarity, finance, maps, recipes, engineering models, classroom ratios, and scientific scaling. A reliable calculator reduces arithmetic errors, speeds comparison work, and helps explain why balanced quantities stay consistent across different sizes.
Frequently Asked Questions
1. What is a proportion in mathematics?
A proportion states that two ratios are equal. For example, 2:3 = 4:6 is a proportion because both ratios represent the same relationship.
2. How does the calculator find a missing term?
It uses cross multiplication. When A/B = C/D, the equality A × D = B × C lets the unknown term be isolated and solved directly.
3. Can I use decimals and negative numbers?
Yes. The calculator accepts integers, decimals, and negative values. Just avoid zero in denominator positions because the ratio would become undefined.
4. What does Equivalent Ratio Check do?
It compares both ratios and their cross products. If A × D equals B × C, the ratios are proportional and represent the same balance.
5. What is Scale Ratio mode useful for?
Scale Ratio mode enlarges or reduces a ratio without changing its relationship. It is useful for recipes, models, classroom groups, drawings, and maps.
6. Why are cross products shown in the result?
Cross products help verify the logic behind the answer. Equal cross products confirm that the completed proportion remains balanced.
7. What does the chart represent?
The chart visualizes the entered terms, solved values, or scaled outputs. It gives a quick visual comparison between ratio parts and validation checks.
8. Can I export the result for reports or class notes?
Yes. Use the CSV button for spreadsheet work and the PDF button for printable records, documentation, handouts, or study files.