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CalcivoTools

Proportion Calculator : Solve Direct & Inverse Proportions (A/B = C/D)

The Calcivo Proportion Calculator solves direct proportions (A/B = C/D) and inverse proportions (A·B = C·D). Enter any three known values to determine the exact unknown fourth variable with step-by-step cross-multiplication.

Interactive Calculator

100% Client-Side Engine
Direct Proportion: A / B = C / D
/
=
/
Leave exactly one box blank or empty to solve for it.
Solved Unknown (D)
D = 100
Proportion Type
direct Proportion
Proportionality Constant (k)
0.5
Derivation Steps
Direct proportion formula: A / B = C / D
Cross-multiplication: 10 × D = 20 × 50
Solve for D: D = (20 × 50) / 10 = 100

Step-by-Step Examples

Direct Proportion: 10/20 = 50/D

Finding missing denominator in scale proportion.

Inputs: A: 10, B: 20, C: 50, D: ?
Result: D = 100

Cross-multiplication: 10 × D = 20 × 50 = 1000 -> D = 1000 / 10 = 100.

How to Use This Tool

  1. Select proportion mode: Direct (A/B = C/D) or Inverse (A·B = C·D).
  2. Enter three known values and leave the target unknown variable blank.
  3. Click Calculate to view the solved variable, proportionality constant, and full derivation.

Frequently Asked Questions

In a direct proportion, as one variable increases, the other increases at a constant ratio (A/B = k). In an inverse proportion, as one increases, the other decreases such that their product remains constant (A × B = k).

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