I am confused between these 2 videos .

In the first videos , it's same as what i learnt in pre-university education course .

When we are calculating kth percentile , the value that we get is whole number , then we need to the use (the value of the current number + value of the next number ) /2

Whereas in the 2nd video , when we are calulating the 20th percentile from 10 number , it's the 2nd number that represent 20% . So , the 20th percentile is the 3rd number , which make sense too .
Because percentile is defined as the percentage of data which is below the value

How to Calculate Percentiles in Statistics - dummies

In this link , it's clear that the first video is correct .
I also learnt this in pre-u courses . So , i think 2nd video is wrong .

Can someone clarify ?