Proportion Solver

Solve a/b = c/d for any unknown

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About Proportion Solver

A proportion solver that finds the missing value in a/b = c/d using cross multiplication. Shows step-by-step solution, verifies the result, and demonstrates scaling applications. Handles direct and inverse proportions. All calculations are client-side. Essential for math students, recipe scaling, map distances, and unit conversion problems.

Proportion Solver Features

  • 4-field solver
  • Cross multiply
  • Step-by-step
  • Verify
  • Scale factor
A proportion states that two ratios are equal: a/b = c/d. If you know three values, cross multiplication finds the fourth: a×d = b×c. Proportions are used in recipe scaling, map reading, model building, pharmacy dosing, and similarity in geometry.

How to Use

Enter any 3 of 4 values:

  • a/b = c/d: Leave one blank
  • Cross multiply: a×d = b×c
  • Solve: Missing value calculated

Cross Multiplication

a/b = c/d → a×d = b×c. If a is missing: a = (b×c)/d. This works because equal fractions have equal cross products.

Real-World Uses

  • Recipe scaling: 2 cups for 4 servings, x cups for 6 servings
  • Map scales: 1 inch = 50 miles
  • Similar triangles in geometry
  • Currency conversion

Step-by-Step Instructions

  1. 1Enter three known values.
  2. 2Leave the unknown field blank.
  3. 3View the solved value.
  4. 4Check the step-by-step solution.
  5. 5Verify the cross products are equal.

Proportion Solver — Frequently Asked Questions

How do I set up a proportion?+

Keep consistent units on each side. If 3 apples cost $2, how much for 9 apples? Set up: 3/2 = 9/x. Cross multiply: 3x = 18, so x = $6.

What is cross multiplication?+

In a/b = c/d, multiply diagonally: a×d = b×c. This eliminates fractions and gives a simple equation to solve.

What's the difference between direct and inverse proportion?+

Direct: as x increases, y increases (y = kx). Inverse: as x increases, y decreases (y = k/x). Speed and time are inversely proportional.

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