# Using super flexible keyword parameters

Some design problems involve solving a simple equation for one unknown when given enough known values. For example, rate, time, and distance have a simple linear relationship. We can solve any one when given the other two.

Here are the three rules that we can use as an example:

*d*=*r*×*t**r*=*d*/*t**t*=*d*/*r*

When designing electrical circuits, for example, a similar set of equations is used based on Ohm's Law. In that case, the equations tie together resistance, current, and voltage.

In some cases, we want to provide a simple, high-performance software implementation that can perform any of the three different calculations based on what's known and what's unknown. We don't want to use a general algebraic framework; we want to bundle the three solutions into a simple, efficient function.