What is the ideal keyword density of a page?
What is the ideal keyword density: 0.7%, 7%, or 77%? Or is it some other number?
There is no ideal keyword density that will guarantee you #1 positioning and this is not the case.
The first few times you mention a word, Google takes notice but after a while using the same word has no additional benefit.
If you use it too much you are in danger of keyword stuffing and this can be counter-productive. If you overuse the keyword and it does not read well then this will drop the positioning.
There is no hard and fast rule on keyword density. Do not buy keyword density software.