descriptive statistics

• Does Standard Deviation Change When You Add or Multiply by a Constant?
  Adding a constant leaves the standard deviation unchanged; multiplying by a scales it by |a| and the variance by a². Proof, examples and the general rule for aX + b.
• How to Find Quartiles from a Histogram (Grouped Data)
  Find Q1, the median and Q3 from a histogram using cumulative frequencies and the grouped-data interpolation formula, with a fully worked example.