<p>Given a date range, I need to know how many Mondays (or Tuesdays, Wednesdays, etc) are in that range.</p>

<p>I am currently working in C#.</p>

Any particular language and therefore date format?
If dates are represented as a count of days, then the difference between two values plus one (day), and divide by 7, is most of the answer.  If both end dates are the day in question, add one.
Edited:
corrected 'modulo 7' to 'divide by 7' - thanks.  And that is integer division.