JAMB Mathematics 2012 Paper

Concept:Standard deviation is the square root of the average of the squared deviations from the mean.Explanation:First, find the mean of the data.$\bar{x} = \frac{2+3+8+10+12}{5} = \frac{35}{5} = 7$.Find each deviation $(x - \bar{x})$ and its square:$2 - 7 = -5$, square $= 25$.$3 - 7 = -4$, square $= 16$.$8 - 7 = 1$, square $= 1$.$10 - 7 = 3$, square $= 9$.$12 - 7 = 5$, square $= 25$.Sum of squared deviations:$25 + 16 + 1 + 9 + 25 = 76$.Divide by the number of values, $n = 5$:Variance $= \frac{76}{5} = 15.2$.Standard deviation $= \sqrt{15.2} \approx 3.9$.Answer:Standard deviation $= 3.9$. Therefore, the correct option is A.