Who knows how to write and read the sign of "weighted average"! Is it X or x?

Who knows how to write and read the sign of "weighted average"! Is it X or x?

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Weighted average
The concept of weighted average
The weighted average is the average of data with different proportions. The weighted average is to calculate the original data according to a reasonable proportion,
If x 1 appears F 1 times, x 2 reappears F 2 times XK appears FK times (n = F1 + F2 +...) Then it's called x1, X2 F 1, F 2 FK is x1, X2 , XK
A simple example is:
Your score in the quiz is 80 and that in the final exam is 90. If the teacher wants to calculate the total average score, he will calculate it according to the proportion of 40% in the quiz and 60% in the final exam, so your average score is:
80×40％+90×60％＝86
There are x people who eat three bowls, y people who eat two bowls and Z people who eat one bowl in the school canteen. How much do you eat on average?
(3*x + 2*y + 1*z)/(x + y + z)
Here, 3, 2 and 1 are weight values respectively, and "weighting" is to consider the proportion of different variables in the population
When some numbers in a group of data repeatedly appear several times, the expression of their average number has changed to some extent. For example, if a person shoots ten times, in which he shoots 10 rings twice, 8 rings three times, 7 rings four times and 9 rings one time, the average number of rings he shoots is
（10*2 + 9*1 + 8*3 + 7*4 ）/10 = 8.1
Here, the four numbers 7, 8, 9 and 10 are the different ring numbers of shooters, but their frequencies are different, they are 4, 3, 1 and 2 respectively. The greater the frequency of data, the greater the influence it has on the average of the whole group of data. In fact, frequency plays a role in weighing data, which is called weight or weight. The above average is called weighted average. It is not difficult to see that the sum of the weights of each data is exactly 10
In weighted average, besides the frequency of a certain number in a group of data is called weight, weight has a broader meaning
For example, in some sports events, the idea of weight should also be used. For example, in diving competitions, each athlete has to complete a certain number of optional actions in addition to the specified actions, and the difficulty of optional actions is different. Because of the different difficulty coefficients of the selected actions, the two players have different scores despite the same quality of their actions, The athletes with high difficulty coefficient should score higher, which actually plays a role of weight
The weights of ordinary arithmetic means are equal, they are all 1, (for example, the average of 3 and 5 is 4), that is to say, they are of the same importance, so the average is a special weighted average
The concept of weighted average
The weighted average is the average of different specific gravity data, expressed in
（4.3）
Here, it represents the weight of each observation value;
Represents the observed value with different specific gravity