Teach 180: The Countdown Begins (Day 141)

This time next month my AP Statistics students will be making sure their calculators have sufficient battery power and will be searching for their #2 pencils.  It is 30 days before the AP Statistics exam and it is the first day of my "Countdown to the AP Statistics Exam Review Tips".  Each day on Twitter I will be posting an exam tip for the next 30 days.  I started this a few years ago and several of my tips are based on my experience as an AP reader.  Many tips are based on common errors and common misconceptions that I have seen on thousands of free-response solutions.  If you are an AP Statistics teacher, feel free to follow my tweets with your class!  Let the Countdown Begin!