Solve proportions using the Rule of 3. Enter three known values in a proportion such as A/B = C/X, and the calculator determines the missing value.
Rule of 3 Calculator
Solve proportions instantly: a / b = c / x
What Is the Rule of 3?
The Rule of 3 is a simple method for solving a proportion when three values are known and one value is unknown.
For example:
6 / 4 = 9 / X
Cross-multiplication gives:
6X = 4 × 9
Therefore:
X = 6
How to Use the Calculator
Enter the three known values:
- A
- B
- C
The calculator treats X as the unknown value and solves:
A / B = C / X
Click Calculate to see the result.
Formula
Starting with:
A/B = C/X
Cross multiply:
A × X = B × C
Then:
X = (B × C) / A
Example
Suppose:
A = 6
B = 4
C = 9
Then:
X = (4 × 9) / 6
X = 6
Where Is the Rule of 3 Useful?
You can use proportions for:
- Unit conversions
- Recipes
- Scaling quantities
- Ratios
- Business calculations
- Percentage problems
- Mathematics homework
Important Note
The known denominator must not be zero. Also, make sure the values are arranged correctly because changing the order of a proportion changes the result.
FAQs
What does the Rule of 3 solve?
It solves a proportion when one of four related values is unknown.
Is the Rule of 3 the same as cross multiplication?
Cross multiplication is the main algebraic step used to solve the proportion.