Yolanda Martinez, age 11, of Colorado Springs, Colo., for her question:

HOW DO WE KNOW HOW MANY PEOPLE WATCH A TV SHOW?

Television sponsors and program directors watch what are called a show's rating. A rating is posted after a  survey is taken that supposedly shows how many people watch various TV programs.

Most important of the rating systems is the Nielsen Survey, conducted by the A.C. Nielsen Co. This company arrives at its rating by determing what programs 1,200 American families watch. The viewing habits of these families, experts in the company say, reflect the habits of the entire nation.

Television networks definitely go along with the ratings. They usually cancel a program if it gets low ratings, and often file cancellation notice after only a few showings of a low rated show.