Mathematics and Statistics

Standard Deviation

A measure of spread: the square root of the average squared distance of data from their mean.

Standard deviation summarises how far a set of values typically lies from its mean, in the same units as the data. Its square is the variance, which carries squared units. A population standard deviation divides the sum of squared deviations by N; a sample standard deviation divides by n − 1, which corrects for estimating the mean from the same data.

For a normal distribution, about 68% of values lie within one standard deviation of the mean, 95% within two and 99.7% within three. Concrete acceptance, survey error and traffic speeds are all described this way, and reading whether a question means a sample or a population is part of the answer.

How much of the FE Civil exam is Mathematics and Statistics?