What is Keyword Density?

a. The number of times the keyword is used / (DIVIDED BY) the total word count on page – (MINUS)the       total words in HTML on the page
b. The number of times the keyword is used X (MULTIPLIED BY) the total word count on page
c. The number of times the keyword is used in the page description
d. The number of times the keyword is used in the page title
e. The number of times the keyword is used / (DIVIDED BY) the total word count on the page