Wikipedia:Reference desk/Archives/Science/2018 July 1

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July 1

Lexell's Comet

I just read the Lexell's Comet article that's currently on the Main Page, and I was confused by the conclusion. In a 2018 paper (DOI: 10.3847/1538-3881/aab1f6), a team examined four asteroids and evaluated whether they could be the remains of the comet; one had a 99.2% chance of being the comet, one had a 74% chance, and the other two had less than 1%. Mathematically, how does this work? Isn't this saying that there's a 173% chance of one of the first two being the comet? I can't imagine such a basic mistake getting past peer-reviewers, so I'm guessing I've misunderstood something. Maybe they said that it broke in pieces, and therefore both of those asteroids could be parts of it? Nyttend (talk) 12:06, 1 July 2018 (UTC)

See Probability#Not_mutually_exclusive_events. You have to subtract the probability that both are remains of the comet, which comes to 0.992×0.74 = 0.734 (assuming the probabilities are independent). Hence the probability that one or the other (or both) are remains is 99.8%. --Wrongfilter (talk) 12:15, 1 July 2018 (UTC)