revisit and update language re: symmetry of box plots / histograms

[retabak]

Symmetry comes up in histogram and box plot lessons. What language do we want to use to acknowledge that the data may not actually be perfectly symmetrical?

• Language about doesn't need to be an exact mirror image
• Data may have greater variability and skew than the box plot or histogram presents (teacher note or note to students - histograms are proxies for the data - histogram overlaid on dot plot)