---
epic: 6
story: 6.5
title: "Proportions / Rule of Three"
status: draft
---

## Epic 6 — Advanced Math & Functions
**Goal:** Scientific, financial, and power-user math.

### Story 6.5: Proportions / Rule of Three

As a **CalcPad user**,
I want to solve proportion problems using natural language,
So that I can quickly compute unknown values in ratios without manually setting up equations.

**Acceptance Criteria:**

**Given** the user writes `3 is to 6 as what is to 10?`
**When** the engine evaluates
**Then** the result is `5`

**Given** the user writes `3 is to 6 as 5 is to what?`
**When** the engine evaluates
**Then** the result is `10`

**Given** the user writes `10 is to 5 as 20 is to what?`
**When** the engine evaluates
**Then** the result is `10`

**Given** the user writes `0 is to 5 as what is to 10?`
**When** the engine evaluates
**Then** the result is `0`

**Given** the user writes `3 is to 0 as 5 is to what?`
**When** the engine evaluates
**Then** an error is displayed (division by zero in the proportion)