# Cross multiplication

Calculate rules of three easily with this tool. You can choose between direct or inverse proportionality, and you can also select whether to solve a simple or double rule of three. The cross multiplication is a mathematical method that allows you to quickly solve proportionality problems.

## Instructions

Enter the three values (if it's a simple rule of three) or the 5 values (if it's double), and immediately, depending on whether the option for direct or inverse proportionality is selected, the result will be calculated and displayed in the corresponding text field for the unknown variable.

## Simple direct rule of three

This rule has two pairs of directly proportional variables. This means that the proportionality ratio (quotient in this case) between the variables in one pair is equal to the proportionality ratio of the other pair.

Solving for the unknown variable, which in this context is D, we get:

## Simple inverse rule of three

Similar to the previous case, we have two pairs of variables; however, this time they are inversely proportional.

Solving for the unknown variable D, we obtain:

## Double direct rule of three

This rule is the extension of the six-variable rule of three in the simple direct case.

## Double inverse rule of three

Finally, we have the equivalent of inverse proportionality from the previous case with six variables.

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