Solve for the missing value in a proportion - A is to B as C is to X.
A proportion states that two ratios are equal: A is to B as C is to x. Solving for the unknown uses cross multiplication, a fundamental technique used in recipes, scaling, unit conversions, and more.
x = (B × C) ÷ A, derived from cross-multiplying A/B = C/x.
If 3 is to 4 as 15 is to x, then x = (4 × 15) ÷ 3 = 20.
Given three of four values in a/b = c/d, it cross-multiplies and solves for the missing value.
For a/b = c/d, cross-multiplying gives a×d = b×c.
Scaling recipes, map reading, and unit conversion all rely on proportional reasoning.