Average yearly inflation. If an item costs C at one time and D nyears later, and Cxn = D, then we call x the averageannual inflation factor (for example, x = 1.04 refers to aninflation rate of 4%).
At a 6% average annual inflation factor, it will take 12 yearsfor the house to double.  If 6% is replaced by r%,bankers use 72/r to estimate the number of years. This is calledthe rule of 72. Graph this estimate and the actual answer over theinterval 1 <= r <= 12. Comment on the accuracy of the rule of72.
