A growth factor is the factor by which a quantity multiplies itself over time. When trying to find the growth rate, you have to remember that the original exponential formula was y = ab^x. You will notice that in these new growth and decay functions, the b value (growth factor) has been replaced either by (1 + r) or by (1 - r). The growth "rate" (r) is determined as b = 1 + r.
