Rule of 3: how to use and solve everyday problems

The rule of 3 is one of the most used mathematical tools in everyday life. It helps discover an unknown value knowing that there is a proportion between two quantities.

Classic examples include proportional increases and reductions, recipe scaling, discounts, and even unit conversions.

Simple rule of 3 example

If 2 shirts cost $50, how much do 5 shirts cost, keeping the same unit price?

Setting up the rule of 3:

2 shirts  →  50 dollars
5 shirts  →   X dollars

The solution is: X = (5 × 50) / 2 = 125. So 5 shirts cost $125.00.

How to use Utilo's Rule of 3 tool

1. Access the Rule of 3 tool.
2. Fill in the three known values.
3. Leave blank the field you want to find.
4. Click Calculate and see the result instantly.

The tool handles the math and allows you to focus only on interpreting the result for your real problem.

Other practical examples

• Scale cooking recipes (double, triple, etc.).
• Find proportional values in budgets.
• Understand proportional adjustments in contracts.