Proportion Solver Formula

Understand the math behind the proportion solver. Each variable explained with a worked example.

Use the Proportion Solver

Formulas Used

X

x = a != 0 ? (b * c) / a : 0

Ratio Left

ratio_left = b != 0 ? a / b : 0

Ratio Right

ratio_right = a != 0 ? c / ((b * c) / a) : 0

Variables

VariableDescriptionDefault
aa3
bb4
cc9

How It Works

How to Solve a Proportion

Setup

a/b = c/x

Cross-Multiplication

a × x = b × c

x = (b × c) / a

Verification

After solving, check that a/b equals c/x.

Worked Example

If 3/4 = 9/x, find x.

a = 3b = 4c = 9
  1. 013/4 = 9/x
  2. 02Cross multiply: 3x = 4 × 9 = 36
  3. 03x = 36/3 = 12
  4. 04Check: 3/4 = 0.75, 9/12 = 0.75

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