For more details on how this rounding works, see https://www.explainxkcd.com/wiki/index.php/2585:_Rounding.
Constructing the Null and Alternate Hypotheses
Fun with units
Fun with statistical significance
Useful geometric formulas
Geometry textbooks always try to trick you by adding decorative stripes and dotted lines.
If you’re having trouble getting the formulas behind the joke, please see https://www.explainxkcd.com/wiki/index.php/2509:_Useful_Geometry_Formulas.
Usefulness of Mathematical Symbols in a Fight