Dr. Brian Keegan:

The ratio does not matter, it is the degree of activity. The actual amount does not matter. Tax does not generally work on de minimis. It does not distinguish as to whether there is 5%, 10%, 15% or 20% which is passive. Generally speaking, it is not often an issue because if a company is trading, it is fairly obvious. If it is buying and selling stuff, manufacturing, or providing services, it is trading.