A certain piece of dubious information about the cancellation of final exams began to spread one day on a college campus with a population of 80,000 students. Assume that initially one thousand students heard the rumor on the radio. Within a day l0.000 students had heard the rumor. Assume that the increase of the number x (in thousands) who had heard the rumor is proportional to the number of people who have heard the rumor and the number of people who have not heard the rumor. Determine x(t).