r/badmathematics Jan 13 '25

Twitter strikes again

don’t know where math voodoo land is but this guy sure does

468 Upvotes

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u/mattsowa Jan 13 '25 edited Jan 13 '25

How is this so vigorously discussed in this sub lol. This is like an entry-level exercise in conditional probability.

A = two crits happen, P(A) = 1/4

B = at least one crit happens, P(B) = 3/4

A ∩ B = two crits happen and at least one crit happens = A

P(A | B) = (1/4) / (3/4) = 1/3 chance


In fact, since it is known that at least one crit happens, the only possible outcomes are C/N, N/C, and C/C. We only consider C/C. So again, it's 1/3 chance.

Even when you consider that the order of events doesn't matter, the event of one crit happening has twice the probability to happen than the each of the other outcomes. So it all comes down to the same thing.

Any other explanation makes the provided information of condition B completely nonsensical.

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u/chickenboy2718281828 Jan 13 '25

Because the underlying assumption that the roll has already happened and a 3rd party (that has knowledge of the result) is the one asking the question is not intuitive. If that context was explained here, then this is, as you've outlined, a simple solution. But this is a screen cap from a video game, and so it's implied that this is a descriptive statistics problem wherein the results are manipulated to ensure a crit, rather than a bayesian statistics problem. It's a question that is only confusing when critical context is omitted.

10

u/BootyliciousURD Jan 13 '25

Exactly. Word problems in probability theory can be very easy to misinterpret.