You get a general formula by looking at what you are doing in general. The first year you invested "A" and at the end of the year had 1.1A. You added another "A" to that to make 1.1A+ A and, at the end of that year had . You added another "A" and so had and, at the end of that year had . Now, it should be easy to see that, at the beginning of the nth year, you have . The part in parentheses isgeometric sum, of the form [/tex]a+ ab+ ag^2+ \cdot\cdot\cdot+ ab^{m-1}+ ab^n[/tex] with a= 1 and b= 1.1. It is well known that this sum is equal to . Here, that would be