Suppose I have an urn with 9 balls: 4 green, 3 yellow and 2 white ones. I draw a ball from the urn repeatedly with replacement. (a) Suppose I draw n times. Let X., be the number of times I saw a green ball followed by a yellow ball. Calculate the expectation Ex, (b) Let y be the number of times I drew a green ball before the first white draw. Calculate E[Y]. Can you give an intuitive explanation for your answer

Respuesta :

Answer:

[tex]E(X_n)=\frac{2(n-1)}{27}[/tex]

[tex]E(y)=\frac{14}{9}[/tex]

Step-by-step explanation:

From the question we are told that:

Sample size n=9

Number of Green [tex]g=4[/tex]

Number of yellow [tex]y=4[/tex]

Number of white [tex]w=4[/tex]

Probability of Green Followed by yellow P(GY) ball

 [tex]P(GY)=\frac{4}{9}*\frac{3}{9}[/tex]

 [tex]P(GY)=\frac{4}{27}[/tex]

Generally the equations for when n is even is mathematically given by

 [tex]Probability of success P(S)=\frac{4}{27}[/tex]

 [tex]Probability of Failure P(F)=\frac{27-4}{27}[/tex]

 [tex]Probability of Failure P(F)=\frac{23}{27}[/tex]

Therefore

 [tex]E(X_n)=\frac{n}{2}*P[/tex]

 [tex]E(X_n)=\frac{n}{2}*\frac{4}{27}[/tex]

 [tex]E(X_n)=\frac{2n}{27}[/tex]

Generally the equations for when n is odd is mathematically given by

 [tex]\frac{n-1}{2}[/tex]

 [tex]E(X_n)=\frac{n-1}{2}*\frac{4}{27}[/tex]

 [tex]E(X_n)=\frac{2(n-1)}{27}[/tex]

b)

Probability of drawing white ball

 [tex]P(w)=\frac{2}{9}[/tex]

Therefore

 [tex]E(w)=\frac{1}{p}[/tex]

 [tex]E(w)=\frac{1}{\frac{2}{9}}[/tex]

 [tex]E(w)=\frac{9}{2}[/tex]

Therefore

 [tex]E(y)=[E(w)-1]\frac{4}{9}[/tex]

 [tex]E(y)=[\frac{9}{2}-1]\frac{4}{9}[/tex]

 [tex]E(y)=\frac{14}{9}[/tex]