Cross Product Calculator (Rule of Three)
The Rule of Three (French: règle de trois) is a method for solving proportions. It's widely used in finance, science, and business calculations where values are proportional.
×
=
×
Understanding the Method
For proportional values a, b, c, and d:
a
b
=
c
d
The cross products are equal:
a × d = b × c
To find any missing value:
- d = (b × c) ÷ a
- c = (a × d) ÷ b
- b = (a × d) ÷ c
- a = (b × c) ÷ d
How to Use
- 1. Enter three known values
- 2. Type 'x' for the unknown value
- 3. The calculator will automatically solve for x
- 4. Results update in real-time as you type
Common Applications
- • Currency conversion rates
- • Recipe scaling
- • Price comparisons
- • Scale calculations
- • Unit conversions
- • Percentage calculations
Practical Example
If 3 apples cost $6, how much do 5 apples cost?
3 apples → $6
5 apples → x dollars
3/6 = 5/x
3x = 6 × 5
x = (6 × 5) ÷ 3 = $10