Rule of Three Calculator
Solve direct proportion problems instantly
Enter Values
Result
Enter values to calculate the result
The solution will appear here with step-by-step explanation
Proportion
Calculation Steps
When to Use Rule of Three Calculator
Recipe Scaling
Scale recipes up or down perfectly. If a recipe for 4 servings needs 2 cups of flour, calculate exactly how much flour you need for 10 servings. Perfect for cooking and baking conversions.
Price Calculations
Calculate costs and prices proportionally. If 3 items cost $15, find out how much 7 items would cost. Useful for shopping, budgeting, and business pricing decisions.
Unit Conversions
Convert between different units of measurement. If 5 kilometers equal 3.1 miles, calculate how many miles are in 12 kilometers. Great for international travel and science.
Math Homework
Solve proportion problems for school assignments. Get step-by-step solutions to understand the process. Perfect for students learning ratios, proportions, and cross-multiplication.
Chemical Mixtures
Calculate chemical concentrations and mixture ratios. If 100ml of solution contains 5g of substance, find how much substance is in 250ml. Essential for chemistry and laboratory work.
Business Forecasting
Project sales, production, and resource needs. If 10 employees produce 500 units, calculate output for 25 employees. Useful for capacity planning and business projections.
Frequently Asked Questions
What is the rule of three calculator?
The rule of three calculator is a mathematical tool that solves direct proportion problems. It helps you find an unknown value (x) when you know three other values in a proportional relationship. The formula is: if a is to b, then c is to x, where x = (b × c) / a. This is commonly used in cooking, unit conversions, business calculations, and solving ratio problems.
How does the rule of three work?
The rule of three works by setting up a proportion: a:b = c:x. To find x, you cross-multiply and divide: x = (b × c) / a. For example, if 2 apples cost $3, how much do 5 apples cost? Set up: 2:3 = 5:x, then x = (3 × 5) / 2 = $7.50. The calculator automatically performs this calculation and shows you the step-by-step solution.
Is this rule of three calculator free?
Yes, our rule of three calculator is completely free to use with no registration required. You can solve unlimited proportion problems, adjust decimal precision, and see detailed calculation steps without any cost. There are no hidden fees, premium features, or usage limits.
What is direct proportion?
Direct proportion means that when one quantity increases, the other increases proportionally, and when one decreases, the other decreases proportionally. The ratio between the two quantities remains constant. For example, if you buy more items, the total cost increases proportionally. The rule of three calculator is specifically designed for direct proportion problems.
When should I use the rule of three calculator?
Use the rule of three calculator for: recipe scaling (if 2 cups serve 4 people, how much for 10 people?), unit conversions, price calculations (if 3 items cost $15, what about 7 items?), speed and distance problems, currency exchange, ingredient proportions, business forecasting, and any situation involving direct proportional relationships.
Can I adjust the decimal precision?
Yes! Our calculator allows you to set the number of decimal places for the result, from 0 to 10 decimal places. This is useful when you need exact precision for scientific calculations or prefer rounded numbers for everyday use. Simply adjust the decimal places setting before calculating.
What is the difference between direct and inverse proportion?
In direct proportion, both quantities increase or decrease together (more workers = more output). In inverse proportion, when one increases, the other decreases (more workers = less time needed). This calculator is for direct proportion only. The formula for direct proportion is x = (b × c) / a, while inverse proportion uses x = (a × b) / c.
Can I use this for cooking and recipe conversions?
Absolutely! The rule of three calculator is perfect for scaling recipes. For example, if a recipe for 4 servings needs 2 cups of flour, how much flour for 10 servings? Enter a=4, b=2, c=10, and get x=5 cups. It works for any ingredient conversion or recipe scaling scenario.
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