A question about “ percentile ”,please help me !!!

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,