According to the Uniform Plumbing Code, the minumum area of any vent installed in a combination waste and vent system shall be at least ____ of the internal crossectional area of the drain pipe serviced.

According to the Uniform Plumbing Code, the minumum area of any vent installed in a combination waste and vent system shall be at least ____ of the internal crossectional area of the drain pipe serviced.