If you're reading this blog, you're probably already familiar with statistics. You probably regard linear regressions and ANOVAs as simple, even if you don't know all of the mathematical details behind them. If that describes you, you may not find Nathan Green's new series on statistics at The Guardian all that useful,1 but if you have friends or relatives who don't understand the difference between the mean of a sample and the mean of the population from which it was drawn or why the difference is important, you might want to encourage them to follow his series.
The first one outlines the challenges associated with sampling. The second one describes different measures of central tendency (mean, median, and mode).2
1But he explains basic ideas very clearly, so it's still worth a look. 2It even mentions geometric and harmonic means, although it doesn't describe how they're calculated or why you might want to use them.