Is a dividend paid as a percentage of the total amount of money invested or as the number of shares you hold?

The dividend is paid as a set amount per share. Be leery of stated yields, always verify exactly what the dividend amount is. If a company grants a special dividend on a one-time basis, it will boost the stated yield but may not really represent what you will be getting going forward. Likewise, dividend increases don't show up in the stated yield until they are paid, so the full increase won't be completely represented in the stated yield until a year has passed.