Find the probability from the expected value?

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SUMMARY

The discussion centers on calculating the probabilities x and y for the random variable Z, given specific values and their probabilities. The values provided are z = 2, 3, 5 with probabilities of 1/6 each, while z = 7 and z = 11 have unknown probabilities x and y. The expected value E(Z) is given as 5 + 2/3. The key equations derived are 7x + 11y = 4 and the requirement that the total probabilities must equal 1, leading to the solution of x and y.

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kylebutler
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Homework Statement



z = 2, P(Z=z)=1/6

z = 3, P(Z=z)=1/6

z = 5, P(Z=z)=1/6

z = 7, P(Z=z)= x

z = 11, P(Z=z)= y

I'm supposed to find x and y given that E(Z)= 5+2/3

I have no idea how to do this. All I got is 7x+11x=4 but I can't solve this
 
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kylebutler said:

Homework Statement



z = 2, P(Z=z)=1/6

z = 3, P(Z=z)=1/6

z = 5, P(Z=z)=1/6

z = 7, P(Z=z)= x

z = 11, P(Z=z)= y

I'm supposed to find x and y given that E(Z)= 5+2/3

I have no idea how to do this. All I got is 7x+11x=4 but I can't solve this

I think you mean you got 7x+11y = 4. To get another equation remember that the Z probabilities must add to 1.
 
LCKurtz said:
I think you mean you got 7x+11y = 4. To get another equation remember that the Z probabilities must add to 1.

Thanks A LOT! How did I not think of that? :-)
 

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