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Mar
25
comment Math of password cracking
Spaces are \, or \;. Your formula looks correct, so if it overestimates then the obvious question is: why do you think it does 4 billion calculations per second? Edit: wait, I may have it. Does your program exit early when it finds the password? Your calculation is the worst case: if the password is generated uniformly and randomly then on average it will take half that time.
Mar
25
reviewed Approve How many different sets of $6$ different numbers can we construct from $11, 13, 18, 19, 19, 20, 23, 25$?
Mar
25
reviewed Leave Open Show that there exist a noncommutative ring (with identity) of order $p^3$.
Mar
25
reviewed Leave Open Find all positive integer $n$ such that there exists $m$ with $2^n-1|m^2+17^2$.
Mar
25
reviewed Close mod operation proof
Mar
25
reviewed Leave Open Use definitions to show $[0, 1) × [0, 1)$ is neither an open nor closed subset of $\Bbb{R^2}$.
Mar
25
reviewed Close why is integration the area under a curve
Mar
25
reviewed Leave Open Quantifier for “there is at most one”?
Mar
24
reviewed Looks OK Partial Fractions as Power Series
Mar
24
reviewed Leave Open For what $n$ does $[\log_21]+[\log_22]+[\log_23]+\dotsb+[\log_2n] = 1538$?
Mar
24
reviewed Leave Open Generalization of the Mobius inversion formula to Dedekind domains
Mar
24
reviewed Leave Open nonzero digits in decimal representation of $\sqrt{2}$
Mar
24
reviewed Reopen permutation & combinations
Mar
24
reviewed Close Number of ways to set 3 queens to attack each other
Mar
24
comment Number of ways to set 3 queens to attack each other
I'm not sure whether the problem statement is intended to be that each queen is attacked by at least one queen or by all other queens; and in the latter case, whether you intend to count "all in a straight line" as an exception.
Mar
24
reviewed Reject Sequences and series of $\tan^n x$
Mar
24
reviewed Leave Closed Home work of PDE
Mar
24
reviewed Close $A\subseteq B\to A\setminus B = \emptyset$. Is this true?
Mar
24
comment $A ⊂ B$ if and only if $A − B = ∅$
The statement is incorrect. Alberto's answer proves the correct statement (with $\subseteq$ instead of $\subset$), but for some reason doesn't point out this important difference.
Mar
24
reviewed Close Do all logic problems have one solution?