-aux.03 P(X-x) find P, find X, from table

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Discussion Overview

The discussion revolves around calculating probabilities and expected values from a given probability distribution table for a discrete variable X. Participants explore the steps to find the value of p when x=2 and the expected value of X in P(X-x).

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant expresses confusion about finding the value of p and the expected value of X.
  • Several participants emphasize that the sum of the probabilities must equal 1.
  • There is a calculation presented for the expected value, with one participant suggesting that p can be calculated as $p=1-(0.4+0.2+0.07+0.02)=0.31$.
  • Another participant confirms the calculation of p as correct and provides a formula for the expected value.
  • One participant mentions obtaining a slightly higher value for the expected value and questions whether rounding is involved due to the discrete nature of X.
  • Another participant clarifies the concept of discrete versus continuous sets, providing an example.
  • There is a discussion about calculator usage and potential errors in calculations, with one participant admitting to entering a wrong value initially.

Areas of Agreement / Disagreement

Participants generally agree on the method to find p and the expected value, but there is some uncertainty regarding rounding and the interpretation of discrete values. The discussion includes both confirmations and corrections of earlier claims without reaching a definitive consensus on all points.

Contextual Notes

Some participants express uncertainty about the implications of discrete versus continuous variables, and there are references to potential rounding issues in calculations, which remain unresolved.

Who May Find This Useful

Individuals interested in probability distributions, expected value calculations, and the nuances of discrete versus continuous variables may find this discussion beneficial.

karush
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The probability distribution of the discrete variable X is given by the following table
https://www.physicsforums.com/attachments/1099

(a) Find the value of p where x=2.
(b) Calculate the expected value of X in P(X-x)

I am basically clueless about this, but is $\mu=3$
 
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a) You want the sum of the probabilities to be 1.

b) $$E[X]=\sum_{k=1}^5x_kP_k$$

What do you find?
 
MarkFL said:
a) You want the sum of the probabilities to be 1.

b) $$E[X]=\sum_{k=1}^5x_kP_k$$

What do you find?

does this mean $p=1-(0.4+0.2+0.07+0.02)=.31$
 
karush said:
does this mean $p=1-(0.4+0.2+0.07+0.02)=.31$

Yes, that's correct.

Now, to find the expect value, find the sum of the products of the x-values and their corresponding probabilities.
 
MarkFL said:
Yes, that's correct.

Now, to find the expect value, find the sum of the products of the x-values and their corresponding probabilities.

$$(1\times0.4)+(2\times.31)+(3\times0.2)+(4\times0.07)+(5\times0.02)=2$$
 
karush said:
$$(1\times0.4)+(2\times.31)+(3\times0.2)+(4\times0.07)+(5\times0.02)=2$$

I get a slightly higher value...are you rounding because $X$ is given as discrete?
 
uhmmm, well, don't recall any rounding. just let the WF compute it.

no sure what is meant by discrete
 
karush said:
uhmmm, well, don't recall any rounding. just let the WF compute it.

no sure what is meant by discrete

Did you recompute and get the same value?

As an example, the set of integers is discrete, while the set of real numbers is continuous.
 
MarkFL said:
I get a slightly higher value...are you rounding because $X$ is given as discrete?

I accidentally entered a wrong value in my calculator...2 is correct.
 
  • #10
MarkFL said:
I accidentally entered a wrong value in my calculator...2 is correct.

no worry, it happens, too often for me even after double checking

just curious what Calc do you have ... I have the TI-Nspire CX CAS.. its really nice
but I go to WF a lot too...

I'll be posting another probability distribution problem next, I seem to be getting the hang of it ... also want to get proficient with box plots

Much Mahalo
 
  • #11
I have a TI-89 Titanium, although in this case I used W|A. Had I used the TI, I might not have made the error as I could have been looking at the data table as I entered the numbers. :D
 

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