Expected number of random variables that must be observed

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Discussion Overview

The discussion revolves around the expected number of random variables that must be observed, focusing on two specific parts: (a) calculating the expected value and (b) addressing a potential typographical error in the formulation of a related expression. The scope includes mathematical reasoning and technical explanations related to probability theory.

Discussion Character

  • Technical explanation, Mathematical reasoning

Main Points Raised

  • Some participants propose that the expected value for part (a) is given by the expression ## \mathbb{E} [N] = p^{-4}q^{-3} + p^{-2}q^{-1} + 2p^{-1} ##.
  • One participant suggests that there is a typographical error in the expression for part (b), indicating that it should be corrected to XN=p-4q-3 - p-3 q-2- p-2 q-1 - p-1.
  • Another participant agrees with the correctness of the answer to part (a) as provided by the original author and acknowledges their own error in a previous response.
  • A later reply expresses appreciation for the method used in the calculations, describing it as brilliant.

Areas of Agreement / Disagreement

Participants generally agree on the correctness of the answer to part (a), while there is a recognition of a potential error in part (b). The discussion reflects some consensus on part (a) but does not fully resolve the issues surrounding part (b).

Contextual Notes

There are indications of typographical errors and corrections, but the exact implications of these corrections remain unresolved. The discussion does not clarify all assumptions or dependencies related to the expressions presented.

WMDhamnekar
MHB
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TL;DR
Expected number of random variables that must be observed before any specific sequence.
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In my opinion, answer to (a) is ## \mathbb{E} [N] = p^{-4}q^{-3} + p^{-2}q^{-1} + 2p^{-1} ##
In answer to (b), XN is wrong. It should be XN=p-4q-3 - p-3 q-2- p-2 q-1 - p-1. This might be a typographical error.
Is my answer to (a) correct?
 
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WMDhamnekar said:
In my opinion, answer to (a) is ## \mathbb{E} [N] = p^{-4}q^{-3} + p^{-2}q^{-1} + 2p^{-1} ##
Please explain your reasoning.

For b) I agree with you.
 
haruspex said:
Please explain your reasoning.

For b) I agree with you.
Answer to (a) given by author is correct. My answer is wrong. Thanks for bringing my error to my notice.
 
WMDhamnekar said:
Answer to (a) given by author is correct. My answer is wrong. Thanks for bringing my error to my notice.
You are welcome.
I had never seen this method before. It's brilliant- thanks for posting.
 
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