title: How can the modulo function be used to work out what day of the week a certain date falls on?
body: <p>Pardon me if it's not the right place to post, but I'm so curious about this.
  So December 5th is a date. Last year it fell on a Tuesday.
  How can modulo be used to work this out?</p>
  
  <p>I know this is a modulo problem, but just don't get how modulo is used here.</p>