Consider the data set
\begin{equation*}
\{2, 5, 8, 10 \}.
\end{equation*}
The 50th percentile should be a numerical value for which approximately 50% of the data is smaller. In this case, that would be some number between 5 and 8. For now, let’s just take 6.5 so that two numbers in the set lie below 6.5 and two lie above. This is a perfect 50% for the 50th percentile. In a similar manner, the 25th percentile would be some number between 2 and 5, say 2.75, so that one number lies below 2.75 and three numbers lie above.