PERCENTILE(array,k)
PERCENTILE function returns the 100*k-th percentile of the given data points (that is, a number x such that a fraction k of the data points are less than x).
Let us assume that the cells A1, A2, ..., A5 contain numbers 11.4, 17.3, 21.3, 25.9, and 40.1. Then
PERCENTILE(A1:A5,0.42) equals 20.02.