It could mean a few different things. I think the answer you are after is regarding the skew of your data set?
I have just started a statistics class and we're given the modal group (-3 to -3.5), mean (-2.92), median (-2.79) and standard deviation (0.630) (talking about grain sizes)
and one of the questions is the mean grain size is not within the size range of the modal group, what does this tell us about the distribution of grain sizes in this sample?
(Thanks for your really fast reply already!)