Answer:
standard deviation sign is σ
mean sign is x , and sometimes it have a hyphen directly above x.
Explanation:
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standard deviation
In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean of the set, while a high standard deviation indicates that the values are spread out over a wider range.
Mean
It is the sum (total) of all the values in a set of data, such as numbers or measurements, divided by the number of values on the list. To find the mean, add up all the values in the set. Then divide the sum by how many values there are.
summation
The symbol ∑ indicates summation and is used as a shorthand notation for the sum of terms that follow a pattern.