While calculating percentile rank there are two formula

1st )

percentile ={ ( number of values below x + 0.5)/total number of observation } *100

2nd )

percentile ={ ( number of values below x )/total number of observation } *100

I have to know when to used 1st formula and when to used 2nd formula

propert explanation needed

1st )

percentile ={ ( number of values below x + 0.5)/total number of observation } *100

2nd )

percentile ={ ( number of values below x )/total number of observation } *100

I have to know when to used 1st formula and when to used 2nd formula

propert explanation needed