The standard deviation of the tap water data is 1.086. The standard deviation of the salt water data is 1.107. Which explains why the standard deviation is the best measure of variability to use to compare the data?

The standard deviation is a statistical tool that measures the degree of spread out of the data in a set. It is calculated from the square root of the variance of of a data set. Standard deviation is the best tool to be used since it takes into account the varying spread about the mean since each data in a set would have different spread with respect to the mean of the data. It tells you the average of the variation of the data from the mean of the population. It divides the data to the upper values from the mean and the lower values from the mean. By this, it would be much easier to make inferences of the data.