**How do you calculate standard deviation of a variable?**
https://www.varsitytutors.com/ap_statistics-help/how-to-find-standard-deviation-of-a-random-variable

There are four steps to finding the standard deviation of random variables. First, calculate the mean of the random variables. Second, for each value in the group (45, 40, 25, and 12), subtract the mean from each and multiply the result by the probability of that outcome occurring. Third, add the four results together.

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