JAMB Mathematics 2013 Paper

Concept:The standard deviation is always the positive square root of the variance of a data set.Explanation:Let the variance be denoted by $\sigma^2$ and the standard deviation by $\sigma$.From the question, we know the variance is $\sigma^2 = 4$.To obtain the standard deviation, take the square root of the variance:$\sigma = \sqrt{\sigma^2} = \sqrt{4}$.Since $\sqrt{4} = 2$, the standard deviation is $2$.The given mean of $5$ is extra information; it is not needed because the variance alone determines the standard deviation.Even if we used the mean to find $x$ and listed the data set, the standard deviation would still be $\sqrt{4} = 2$.Answer:B. $2$