Returns the mean of a set of numbers, ignoring a proportion of high and low values.
numberlist is a range or array of numbers, not necessarily in order. TRIMMEAN returns the mean, ignoring a fraction (0 <= fraction < 1) of the outermost values in numberlist.
Specifically, where n is the count of numbers in numberlist, the highest and lowest INT(n * fraction / 2) values are ignored.
returns the mean of the values in cells A1:A100, ignoring the lowest 5 values and the highest 5 values.