I have tried this problem for several days and do not know the formula to use to solve it. Here is the problem
1. Little Mark was given $10,000 at birth from various family members to be invested until his adulthood. The DOW JONES has averaged an annual average growth rate of 10% for the 20th century. If Little Mark invests his $10,000 in a good solid DOW JONES mutual fund which averages 10% growth per year, and then after the first year and every year thereafter ADDS $1000 per year of his own money, how many years will it take for Little Mark to become a millionaire?

Have you tried using a series?

I don't think there's a nice tidy formula for this problem. You can construct a series like this:



and try and find a value for N that works. You could set this up on a spreadsheet pretty easily.

A spreadsheet was the first thing I did to test the formula I came up with. It was very slightly off though. The series was the only way I could think of doing it. Wanted to see if the OP had thought of using that before giving further help.