Six students in a made-up study group score 4, 6, 7, 9, 10 and 12 marks in a short quiz…

Step 1. Count. $\binom{6}{3} = 20$ samples.

Step 2. The extremes. The lowest three give $\dfrac{4 + 6 + 7}{3} = \dfrac{17}{3} \approx 5.67$ marks. The highest three give $\dfrac{9 + 10 + 12}{3} = \dfrac{31}{3} \approx 10.33$ marks.

Step 3. The population mean. $\dfrac{48}{6} = 8$ marks.

Step 4. Close samples. Listing all $20$ means, $12$ of them lie from $7$ to $9$ marks. None is exactly $8$.