Mean of 4, 8, 6, 10, 12:

💡 Sum ÷ count.

Median of 23, 17, 19, 25, 14, 21, 18:

💡 Sort first.

Standard deviation of 2, 4, 4, 4, 5, 5, 7, 9:

💡 Find mean first, then √(mean of squared deviations).