many blogs say that k=10 is the most commonly number of folds in cross validation. But what is the mathematical explanation behind?

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    $\begingroup$ Possible duplicate of Choice of K in K-fold cross-validation. In short, there are some advantages to having around $k=10$ folds, but the exact number of $10$ has no special benefit over, say $9$ or $11$. $\endgroup$ – Frans Rodenburg Jul 21 '19 at 3:57