4.38 Attendees at an industrial trade show are given the opportunity to fill out a card that entitles them to receive a free software package from the sponsoring firm. The cards are placed in a bin, and 30 winners will be drawn.

Considering the 30 winners as a sample from all of the persons filling out such cards, is this a probability sample or a nonprobability sample? What specific type of probability or nonprobability sample does this procedure represent?