What is the population standard deviation of the data set 4, 8, 6, 10, 12? (Round to the nearest hundredth.)

First find the mean: $\frac{4+8+6+10+12}{5}=\frac{40}{5}=8$. The squared deviations from the mean are $16, 0, 4, 4, 16$, which sum to $40$ and average to $\frac{40}{5}=8$. The standard deviation is $\sqrt8\approx2.83$, choice G. Choice H ($8.00$) is the variance, not its square root. Choice J ($3.16$) divides the sum of squares by $4$ instead of $5$, which is the sample standard deviation formula. Choice F ($2.00$) is not the result of either calculation. The ACT treats a data set given in full as the population.