The m-th percentile is the value before which are m% of the smallest values. Its position is given by the formula:
Position_m = m * (N+1)/100
where N is the size of the sample.
Then, since this sample has N = 14, the 8th percentile will be located at position P8:
Position_8 = 8 * (14 + 1)/100 = 8 * 15/100 = 120/100 = 1.2 =
This means it will be located between the first and second smallest elements.
Since the two smallest elements are 17 and 21, the 8th percentile will be 17 plus D, where
D = 0.2