Inputs
Adjust the assumptions to match your scenario. Results update instantly.
Results
Primary outputs and comparison insights are built from the current inputs.
Solved X
15
Missing fourth value that keeps the proportion balanced.
Scale factor
2.5
Multiplier from A to B within the proportion.
Cross product
60
Shared cross-product value after solving the proportion.
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How this calculator works
The Proportion Calculator solves a missing value in a four-term proportion and also shows the scale factor connecting the known terms. Enter a, b, and c to estimate solved x, scale factor, and cross product. The calculator updates instantly and adds a comparison table plus chart so you can test the sensitivity of the result before you use it in a decision.
Quick guide
Jump straight to the section you need, then return to the calculator.
Inputs
- First known value on the left side of the proportion.
- Second known value paired with A in the proportion.
- Third known value used to solve the missing fourth term.
Outputs
- Missing fourth value that keeps the proportion balanced.
- Multiplier from A to B within the proportion.
- Shared cross-product value after solving the proportion.
Assumptions
- A cannot be zero when solving the proportion this way.
- All four terms belong to the same proportional relationship.
Tips
- Use proportions for scale drawings, recipes, and unit-rate style problems.
- If the answer looks off, check whether the terms were placed in the right order.
Formula guide
Use these formulas to audit the output or explain it to someone else.
2 formulas
Usage examples
Review a ready-made scenario, copy it, then tweak inputs to match your case.
Example
Recipe scaling example
Inputs
- Example input A: 2
- Example input B: 5
- Example input C: 8
Outputs
- Example result Solved X: 20
- Example result Scale factor: 2.5
- Example result Cross product: 40
Proportion solving is quick, but getting the term order right is what usually determines whether the answer makes sense.
Solved value by C
| C | Solved X | Scale factor |
|---|---|---|
| 3 | 7.5 | 2.5 |
| 5 | 12.5 | 2.5 |
| 6 | 15 | 2.5 |
| 8 | 20 | 2.5 |
| 10 | 25 | 2.5 |
Proportions scale linearly, so if A and B stay fixed the solved value moves directly with C.
Proportion result sensitivity
Focus point
3
7.5
Position
#1 of 5
Original order
Share of total
9.38%
Total: 80
Proportions scale linearly, so if A and B stay fixed the solved value moves directly with C.
References
- Proportion solving by cross multiplication
- Scale-factor reasoning in elementary algebra
FAQ
Common questions
What does the Proportion Calculator do?
The Proportion Calculator solves a missing value in a four-term proportion and also shows the scale factor connecting the known terms. Enter a, b, and c to estimate solved x, scale factor, and cross product. The calculator updates instantly and adds a comparison table plus chart so you can test the sensitivity of the result before you use it in a decision. It is part of our math toolkit.
What inputs do I need?
Typical inputs include First known value on the left side of the proportion., Second known value paired with A in the proportion., Third known value used to solve the missing fourth term..
How are the results calculated?
We follow the formulas and assumptions outlined in the "How this calculator works" section. You will see outputs like Missing fourth value that keeps the proportion balanced., Multiplier from A to B within the proportion., Shared cross-product value after solving the proportion..
Can I share or download the results?
Use the Copy link or Print buttons to share your results. If a table or chart appears, you can download the data as CSV.
Is my data stored?
No. Calculations run in your browser and we do not store your inputs.
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