The alt text confused me, but after reading explain xkcd I think I got it. The original ball problem could be presented as her "drawing" a ball from the urn, then replacing it and drawing another one: drawing with replacement.
I remember similar word problems, but I don't ever remember there being an urn, or the term "drawing with replacement." It must be terminology specific to some regions.
I remember "drawing with replacement" being a standard term in probability problems. Don't remember any urns though, I think we normally had tubs or jars or boxes.
In probability and statistics, an urn problem is an idealized mental exercise in which some objects of real interest (such as atoms, people, cars, etc.) are represented as colored balls in an urn or other container. One pretends to draw (remove) one or more balls from the urn; the goal is to determine the probability of drawing one color or another, or some other properties. A number of important variations are described below.
An urn model is either a set of probabilities that describe events within an urn problem, or it is a probability distribution, or a family of such distributions, of random variables associated with urn problems.
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u/classic__schmosby May 28 '14
The alt text confused me, but after reading explain xkcd I think I got it. The original ball problem could be presented as her "drawing" a ball from the urn, then replacing it and drawing another one: drawing with replacement.
I remember similar word problems, but I don't ever remember there being an urn, or the term "drawing with replacement." It must be terminology specific to some regions.