# Fourth, Mean and Third Proportional

### Fourth Proportional

The fourth proportional is any of the terms of a ratio.

### Mean Proportional

A continued proportion has two equal means.

To calculate the proportional mean of a continued proportion, extract the square root from the product of the extremes.

### Third Proportional

In a continued proportion, the third proportional is the variable in a proportion with two equal terms.

A third proportional is equal to the square of the equal terms, divided by the unequal term.