Rule of three
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Find a number in the same ratio to a given number
- Downloads
- 55+
- on Google Play
- Price
- Free
- No in-app purchases
- Updated
- Sep 27
- 2026 · v1.0.1
Screenshots
About Rule of three
Calculator for finding a number in the same ratio to a given number as exists between two other given numbers
With this App you can calculate Rule/Method of Three in a way that you wish, by percentage, whatever!
And doesn't matter the field, it shows the result in any field.
This App calculates proportions (direct), also known as "rule of three" by entering three known values and hitting "Calculate". The App will calculate the missing value for you!
The Rule of Three is a Mathematical Rule that allows you to solve problems based on proportions. By having three numbers: a, b, c, such that, ( a / b = c / x), (i.e., a: b :: c: x ) you can calculate the unknown number.Dec 12, 2016
The Rule of Three is a Mathematical Rule that allows you to solve problems based on proportions. By having three numbers: a, b, c, such that, ( a / b = c / x), (i.e., a: b :: c: x ) you can calculate the unknown number. The Rule of Three Calculator uses the Rule of Three method to calculate the unknown value immediately based on the proportion between two numbers and the third number.
The working of the Rule of Three Calculator can be expressed as follows:
How does the Rule of Three Calculator work?
Simply fill in the fields of the Maths Calculator with the values you want to work out (Value A, Value B and Value X), press the calculate button and the Rule of Three Calculator will immediately display the missing value of Y.
The rule of three is the name of a simple calculation which enables you to calculate something in three steps (hence the name). It is often used because you don't need to know any formulas to do it. The principle is very simple: Do the same stuff on both sides to get to your result.
An example of the Rule of Three:
An example that you would use to explain the rule of three is as follows:
If I have 8 litres of paint for 2 bedrooms, how many litres of paint would I need for 5 bedrooms?
In this case, the two values of a and b are known, a=2 bedrooms and b=8 litres. The value of c is also known ( 5 bedrooms) and the missing value is that of x ( the number of litres) So:
a)2 bedrooms -> b)8 litres
so c)5 bedrooms -> (x=20) litres
x= c*b/a= 8*10/2 = 20 littres
With this App you can calculate Rule/Method of Three in a way that you wish, by percentage, whatever!
And doesn't matter the field, it shows the result in any field.
This App calculates proportions (direct), also known as "rule of three" by entering three known values and hitting "Calculate". The App will calculate the missing value for you!
The Rule of Three is a Mathematical Rule that allows you to solve problems based on proportions. By having three numbers: a, b, c, such that, ( a / b = c / x), (i.e., a: b :: c: x ) you can calculate the unknown number.Dec 12, 2016
The Rule of Three is a Mathematical Rule that allows you to solve problems based on proportions. By having three numbers: a, b, c, such that, ( a / b = c / x), (i.e., a: b :: c: x ) you can calculate the unknown number. The Rule of Three Calculator uses the Rule of Three method to calculate the unknown value immediately based on the proportion between two numbers and the third number.
The working of the Rule of Three Calculator can be expressed as follows:
How does the Rule of Three Calculator work?
Simply fill in the fields of the Maths Calculator with the values you want to work out (Value A, Value B and Value X), press the calculate button and the Rule of Three Calculator will immediately display the missing value of Y.
The rule of three is the name of a simple calculation which enables you to calculate something in three steps (hence the name). It is often used because you don't need to know any formulas to do it. The principle is very simple: Do the same stuff on both sides to get to your result.
An example of the Rule of Three:
An example that you would use to explain the rule of three is as follows:
If I have 8 litres of paint for 2 bedrooms, how many litres of paint would I need for 5 bedrooms?
In this case, the two values of a and b are known, a=2 bedrooms and b=8 litres. The value of c is also known ( 5 bedrooms) and the missing value is that of x ( the number of litres) So:
a)2 bedrooms -> b)8 litres
so c)5 bedrooms -> (x=20) litres
x= c*b/a= 8*10/2 = 20 littres
What’s new
Version 1.0.1 · Updated September 27, 2026
• Learn the method: a new in-app guide covering what the Rule of Three is, two ways to solve it, everyday uses, and where it came from • Worked examples: three problems solved step by step, plus the per-unit method side by side • Renamed to "Rule of three", with a fresh icon and start-up screen • Better readability throughout
User reviews
very nice app to calculate proportions/ It helps you increase your understanding in solving the rule-of-three I like the feature of keeeping A history of calculated values that you can managed within the App.
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