To my understanding, one of these should be correct, the rest are meant to confuse and wrong on purpose. Which one is the correct formula, and what is it used to calculate? This is from my statistics exercises
I can only see 38 to 43. Among them, 39 and 43 are definitely right, 40 is also right if (f_1+f_2+...+f_k=n).
For assurance, you can check the formulas for sample standard deviation.