Rule of Three Calculator
Solve proportions instantly with our Rule of Three calculator. Enter three values to find the fourth unknown value.
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As
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Formula Applied:
X = (B × C) ÷ A
X = (20 × 30) ÷ 10 = 60
What is the Rule of Three?
The Rule of Three is a mathematical method for finding a fourth, unknown value when three values are known and they are proportional. It is widely used for solving problems related to percentages, ratios, scaling recipes, and currency conversion.
Example
If 5 apples cost $2, entering those values plus a quantity of 8 apples calculates a cost of $3.20 using direct proportion.
Common Use Cases
- Scaling a recipe up or down while keeping ingredient ratios consistent.
- Solving proportion word problems for school or work.
FAQs
What's the difference between direct and inverse proportion?
In direct proportion, both values increase together (more apples cost more); in inverse proportion, one value increases as the other decreases (more workers means less time to finish a job).