Calculate spread

Calculate different measures of spread: range, quartiles, interquartile range (IQR), percentiles.

Any value of n may be expected, so that required bounds (e.g. quartiles) may or may not be values in the data set. Alternative methods will be acceptable provided that the method used is clear from the working.
(e.g. if the median lies between two data values the arithmetic mean of these two values may be used.)