WAEC Mathematics 2012 Paper

Concept:Standard deviation is the square root of the average of the squared deviations from the mean.Explanation:The mean is given as $\overline{x} = 21$.For each score $x$, find the deviation $x - \overline{x}$ and its square $(x - \overline{x})^2$:$15 - 21 = -6$, square $= 36$$21 - 21 = 0$, square $= 0$$17 - 21 = -4$, square $= 16$$26 - 21 = 5$, square $= 25$$18 - 21 = -3$, square $= 9$$29 - 21 = 8$, square $= 64$Sum of squared deviations: $36 + 0 + 16 + 25 + 9 + 64 = 150$.Number of scores: $N = 6$.Variance: $\frac{150}{6} = 25$.Standard deviation: $\sqrt{25} = 5$.Answer:The standard deviation of the scores is $5$.Therefore, the correct option is C.