Bank interest

[darkswordmen]

I put $100 into the bank. Every year the bank give a 5% interest. How long must I take to double my money if I take the money out every year and put it in again?

[Didwot]

Assuming the interest is paid annually, and is net of all taxes and charges, and that you reinvest the capital and interest every year then the answer is just over 18 years.
You can work it out quite easily on a spread sheet, and with more effort using a calculator. I expect oneeyedvic will give chapter and verse, as he knows everything about interest calculations.