The standard deviation is a measure of how spread out the data is from the mean. To calculate the standard deviation, we first find the mean of the data set, which is the sum of all the numbers divided by the total number of numbers. In this case, the mean is 81.9. Then, we subtract the mean from each data point, square the result, and sum all the squared differences. Next, we divide the sum by the total number of numbers minus 1, and finally, take the square root of the result. In this case, the standard deviation is 27.5.