Rule of three

The rule of three is a simple method to find a missing number when you know three other numbers in a proportional relationship. It's a tool for accurately adjusting recipes, budgets, or even plans, demonstrating its versatility and practicality in problem-solving.

Rule of Three Calculator

Value 1

Value 2

Value 3

([value3]*[value2])/[value1]

Result

How to Calculate Using the Rule of Three

x = (b * c) / a

Two Practical Rule of Three Examples

Rule of three example 1: Cooking Recipe Adjustment

Imagine you have a recipe that serves 4 people, but you need to adjust it to serve 6 people instead. If the original recipe calls for 2 cups of flour for 4 people, how much flour would you need for 6 people? Using the rule of three:

For 4 people, you need 2 cups of flour.
For 6 people, you need X cups of flour.

Calculation:

X = (6 * 2) / 4 = 3

So, you would need 3 cups of flour to adjust the recipe for 6 people.

Rule of three example 2: Travel Distance and Fuel Consumption

Imagine your car consumes 5 liters of fuel to travel 100 kilometers. How much fuel would you need to travel 150 kilometers? Again, you can use the rule of three:

For 100 kilometers, you need 5 liters of fuel.
For 150 kilometers, you need X liters of fuel.

Calculation:

X = (150 * 5) / 100 = 7.5

Thus, you would need 7.5 liters of fuel to travel 150 kilometers.