Solve proportions of the form A/B = C/D | Find the missing value using cross multiplication
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Missing Value
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📝 Step-by-step solution
Enter three values and click solve.
📖 How it works
For proportion A/B = C/D, cross multiply: A × D = B × C. Then solve for the missing variable.
📖 How to Use This Proportion Calculator
1
Enter three values - Fill in any three of the four fields (A, B, C, or D).
2
Leave one field empty - The empty field is where the calculator will find the missing value.
3
Click "Solve Proportion" - Get the missing value with step-by-step cross multiplication solution.
📐 What is a Proportion?
A proportion is an equation stating that two ratios are equal. It is typically written in the form A/B = C/D, where A, B, C, and D are numbers (with B and D ≠ 0). Proportions are used extensively in mathematics, science, cooking, scaling, map reading, and everyday problem-solving.
If three values are known, the fourth can be found using cross multiplication: A × D = B × C.
🧮 Cross Multiplication Method
If A/B = C/D, then A × D = B × C
To solve for each variable:
• A = (B × C) ÷ D
• B = (A × D) ÷ C
• C = (A × D) ÷ B
• D = (B × C) ÷ A
💡 Real-World Applications of Proportions
Recipes & Cooking: Scaling ingredients up or down
Maps & Scale Drawings: Converting distances
Unit Conversion: Converting between measurement systems
Percentages: Finding part, whole, or percent
Similar Figures: Solving for unknown lengths
Currency Exchange: Converting money between currencies
Speed & Distance: Rate problems
💡 Tips for Solving Proportions
Always identify which variable is unknown first
Write the proportion clearly as A/B = C/D
Cross multiply: multiply across the equal sign
Divide both sides to isolate the unknown variable
Check your answer by plugging back into the original proportion
❓ Frequently Asked Questions
What does "solve a proportion" mean?
Solving a proportion means finding the missing value when two ratios are stated as equal. For example, if 3/4 = 6/x, solving tells us that x = 8.
Can denominators be zero?
No, denominators (B and D) cannot be zero in a valid proportion because division by zero is undefined. The calculator will show an error if you attempt to solve with a zero denominator.
What if I fill all four fields?
If you fill all four fields, the calculator will verify whether the values form a valid proportion (i.e., check if A/B equals C/D).
Does the calculator work with decimals and fractions?
Yes! The calculator accepts decimals (e.g., 2.5) and will return precise results. For fractions, convert to decimal first or use the fraction calculator.
What is the difference between a ratio and a proportion?
A ratio compares two quantities (e.g., 3:4). A proportion states that two ratios are equal (e.g., 3/4 = 6/8).