My guess would be it's due to connection issues, i.e. packet loss or if your computer is slow it may take a while to open a new HTTPS pipe when the keep-alive expires for the graphics pipes. You have well more than 10 seconds to answer it, so it shouldn't be a problem.
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Computing the probability that at least one of the following events will occur:
P(a or b ... or z) = 1 - P(!a and !b ... and !z)
Probability
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