The bureau of justice statistics reports that the number of americans on probation increased 76% from 1980 to 1995 and that 3.09 million americans were on probation in 1995. if the rate of increase continues in the same way for the next 15-year period, what might be the number of americans on probation in 2010?

For this case, what we are going to do is first define variables.
 x: current number of Americans.
 y: number of Americans after the next 15 years.
 We now write the expression to model the problem, assuming:
 "the rate of increase continues in the same way for the next 15-year period".
 We have then:
 y = 1.76 * x
 y = 1.76 * (3.09)
 y = 5.44 million Americans
 
 the number of Americans on probation in 2010 might be:
 y = 5.44 million Americans