Where to find out the method used for excel functions

A     B      C    D
 1     1      0%    1    =PERCENTILE($A$1:$A$6,B1)
 2     2     20%    2    =PERCENTILE($A$1:$A$6,B2)
 3     3     40%    3    =PERCENTILE($A$1:$A$6,B3)
 4     4     60%    4    =PERCENTILE($A$1:$A$6,B4)
 5     5     80%    5    =PERCENTILE($A$1:$A$6,B5)
 6     6    100%    6    =PERCENTILE($A$1:$A$6,B6)
 7
 8           10%    1.5  =PERCENTILE($A$1:$A$6,B8)
 9           11%    1.55 =PERCENTILE($A$1:$A$6,B9)
10           12%    1.6  =PERCENTILE($A$1:$A$6,B10)