How the numbers crunch GM.(News)(Brief Article)

Byline: Dave Guilford

A close look at General Motors' year-end sales prospects shows how difficult it will be for the automaker to finish with a 28.7 percent market share.

In 2003, GM expects U.S. light-vehicle sales to total 16.7 million units.

Through October, GM, Saab and Hummer sold 3,912,120 cars and …