... The following lessons are designed to review the basic mathematical concepts that you will encounter on the GMAT Quantitative section and are divided into three major sections: arithmetic, algebra, ... for a commit-tee.StatisticsMean is the average of a set of numbers. To calculate the mean, add all the numbers in the set and divide by the number of numbers in the set. Find the mean of 2, ... and 15. The mean is 7.Median is the middle number in a set. To find the median, first arrange the numbers in order and thenfind the middle number. If two numbers share the middle, find the average...