book 1 ，reading 3，LOS 7.f: Calculate and interpret quartiles, quintiles, deciles, and percentiles ，

The formula for the position of the observation at a given percentile, y, with n data points

sorted in ascending order is : **Ly = (n + 1) y/100*

is it correct ？

in my opinion ，the formulation should be：Ly=（n-1）*y/100 + 1，