2. Estimated average value: the median value of each group of values in the frequency distribution histogram is multiplied by the frequency and then added.
3. Weighted average: The weighted average is the sum of all frequencies multiplied by the numerical value.
4. Median: the abscissa of a straight line parallel to the Y axis, which divides the frequency distribution histogram into two parts with equal areas.
5. In the rectangular coordinate system, the horizontal axis represents the continuous available values of the sample data. According to the minimum and maximum values of the data, the sample data are divided into m groups, so that the maximum and minimum values fall within the open interval (a, b), where a is slightly smaller than the minimum value of the sample data and b is slightly larger than the maximum value of the sample data. The interval between groups is d=(b-a)/m, and the boundary range of each data group is left closed and right opened, such as [a, a+d], [a+d, a+2d), ... [a+(m- 1) d, b).
6. The vertical axis represents the value of frequency divided by group distance (the number of sample data falling in each group is called frequency, and the frequency divided by the total number of samples is frequency), and the rectangle with the quotient of frequency and group distance as the high and the group distance as the bottom is represented in rectangular coordinate system.