Proportion Calculator

Solve proportions and find missing values in ratios. Enter three known values and find the fourth using cross multiplication.

A

B

C

D

Leave one field empty to solve for that value

Understanding Proportions

Definition

A proportion states two ratios are equal. In the form A/B = C/D, cross multiplication gives A × D = B × C.

Cross Multiplication Method

A/B = C/D ⇒ A × D = B × C

Common Applications

Recipe scaling and cooking measurements
Map scales and distance calculations
Currency exchange and unit conversions
Similar triangles in geometry
Dilution calculations in chemistry

Example Problems

Example 1: If 3 apples cost $2, how much do 12 apples cost?

Setup: 3/2 = 12/x, solving gives x = $8

Example 2: A recipe calls for 2 cups flour for 3 cups sugar. How much flour for 9 cups sugar?

Setup: 2/3 = x/9, solving gives x = 6 cups flour

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