What is the probability of pulling a Z in Scrabble?

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Discussion Overview

The discussion revolves around calculating the probability of drawing a specific letter, Z, from a bag of Scrabble tiles. Participants explore different scenarios based on the number of tiles and the presence of the letter Z, considering both basic probability and more complex situations involving unseen tiles.

Discussion Character

  • Exploratory, Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant describes a scenario where they need to calculate the probability of drawing a Z from a bag of seven letters, with one being a Z.
  • Another participant asserts that if there is exactly one Z in the bag, the probability of drawing it is 3/7.
  • A different viewpoint suggests that if there are additional unseen tiles, the probability changes, proposing that with 21 tiles total and one Z, the probability would be 3/21, or 1/7.
  • Some participants discuss the complexity of drawing tiles sequentially, with one suggesting that the probability could be calculated as 1/7 for the first draw, and then adjusting for subsequent draws, leading to a total of 3/7.
  • One participant expresses surprise at the simplicity of the calculation, indicating that their group had overcomplicated the problem.
  • Another participant breaks down the probability calculation step-by-step, showing how to arrive at the 3/7 probability through sequential draws.

Areas of Agreement / Disagreement

Participants present multiple competing views on how to calculate the probability, particularly regarding the impact of unseen tiles and the method of drawing. There is no consensus on a single approach or outcome.

Contextual Notes

Participants reference different scenarios involving varying numbers of tiles and the presence of multiple Zs, indicating that assumptions about the total number of tiles and their distribution significantly affect the calculations.

JoeTrumpet
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I was playing Scrabble with a few friends last night and, as none of us have quite yet learned the ways of prob & stats, we were debating how to calculate the probability of this scenario: I had just formed a word and had to pull three letters out of a bag containing seven letters. One of the letters was surely a Z. What was my probability of pulling out that Z (which, by the way, I did)?

As I've never covered any prob & stats in years (and even then it was covered in just one class day), I wasn't sure how to even begin this. Thanks in advance for helping solve this crucial problem!
 
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Since there was exactly one z in the bag, the probability is simply 3/7.
 
If exactly one tile in the bag (out of 7) was a Z, then 3/7.

But if there were, say, 21 tiles you hadn't seen (2 other players), and you only knew that one of those was a Z, then it would be 3/21 = 1/7. Similarly with other numbers of tiles.

If you had more than one Z, it would get slightly more complicated.
 
Wow, that's a lot easier than we thought it would be. Originally I thought maybe 3/7, but my friends stated that perhaps it would alter it because technically if you take out one at a time it would be 1/7, then 1/6, then 1/5, but they didn't know what to do with those. Definitely overcomplicated it! Thank you very much :)
 
Since you wanted to break it down, let's do it.

You can produce it on the first go: 1/7 chance, and then afterwards doesn't matter what you draw.

You can get it on the second: to do this you need to draw any of the other 6 first,a 6/7 chance, then draw the z which is now 1/6, so the probability is (6/7)*(1/6)=1/7.

You get it with the third tile: 6/7 * 5/6 *1/5 = 1/7.

Add 'em all up and you get 3/7.
 

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