Question about Statistical Concepts and Market Returns

The following ten observations are a sample drawn from a normal population: 25, 20, 18, -5, 35, 21, -11, 8, 20, and 9. The fourth quintile (80th percentile) of the sample is ?

Formula: L§ = n+1 * P/100 where P = 80%, n =10 This results in 8,8

Now take the 8th and 9th value in ascending order which is 21 and 25.

The 8,8 value is 21 + 80% between 21 and 25


^ The solution to this problem on the CFA mock is 21 and it states that it should be the 8th number, which I believe is wrong. I got the same result as you.

I’ve found a handful of errors in their explanations to the mock questions (e.g, trade credit forumla) but this is the first time I remember seeing a wrong answer completely. Or are we both wrong? Now I’m just confused.

I asked this same question, appearantly there is a difference between a sample and a population in this question – there was a thread on this forum with an explination, I didn’t find it all that helpful altough