Given the exponential model:
Where A is the initial condition, b is the growth factor and x is a time-like variable.
We know that the growth factor is 1.9 and that 1500 people died of AIDS in 1983. If we make x to be the years passed since 1983, then 1500 is our initial condition (because 0 years passed). In our model:
For 2005, x = 22: