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There are n+1participants in a game. Each person independently is a winner with probability p. The winners share a total prize of 1 unit. (For instance, if 4 people win, then each of them receives 14whereas if there are no winners, then none of the participants receives anything.) LetAdenote a specified one of the players, and let Xdenote the amount that is received by A.

(a) Compute the expected total prize shared by the players.

(b) Argue that E[X]=1(1p)n+1n+1

(c) Compute E[X]by conditioning on whetherAis a winner, and conclude that E(1+B)-1=1-(1-p)n+1(n+1)p

When Bis a binomial random variable with parameters nand p.

Short Answer

Expert verified

a) The expected total prize shared by the player isE[W]=1-(1-p)n+1

b) The required expression is, E(X)=1-(1-p)n+1(n+1)

c) Computing E[X]by conditioning on whether Ais a winner, and conclude thatE(1+B)-1=1-(1-p)n+1(n+1)p.

Step by step solution

01

Given Information (Part a)

The probability of each person winning the game is, p.

The number of players in the game is,(n+1).

The probability of the no winner of the game is,(1-p)n+1

Let W=0denote the no winner in the game

Let W=1denote the at least one winner in the game.

02

Explanation (Part a) 

Find the expected total prize shared by the players,

E(W)=P(W=1)

=P(At least one winner of the game)

=1-P(No winner of the game)

=1-(1-p)n+1

03

Final Answer (Part a) 

Hence, the required value is1-(1-p)n+1.

04

Given Information (Part b)

The probability of each person wins the game is,p.

The number of players in the game is, (n+1).

The probability of the no winner of the game is,(1-p)n+1

Let W=0denote the no winner in the game

Let W=1denote the at least one winner in the game.

05

Explanation (Part b) 

Let Widenote the prize of the ithplayer.

Each and every player wins independently and has equal probabilities.

From part (a),

1(1p)n+1=E(W)

1(1p)n+1=i=1n+1Wi

localid="1647500883344" EWi=E(X)is the expected prize of playerlocalid="1647500893021" A,

localid="1647500947723" 1(1p)n+1=(n+1)E(X)

localid="1647500955566" 1(1p)n+1(n+1)=E(X)

06

Final Answer (Part b) 

Hence, the required expression is,E(X)=1-(1-p)n+1(n+1).

07

Given Information (Part c) 

The probability of each person winning the game is, p.

The number of players in the game is,(n+1).

The probability of the no winner of the game is,(1-p)n+1

Let W=0denote the no winner in the game

Let W=1denote the at least one winner in the game.

08

Explanation (Part c)

Find the E(X)by conditioning on whether Ais winner.

Let Bfollows a Binomial random variable with parameter(n,p).

Let Y=1鈥呪赌呪赌呪赌ifAwins0鈥呪赌呪赌呪赌Otherwise

E(X)=E[E[XY]]

E(X)=E[XY=0]P(Y=0)+E[XY=1]P(Y=1)

E(X)=0+E(1+B)1(p)

E(X)=E(1+B)1(p)

E(X)p=E(1+B)1

From part (b) Calculation,

1(1p)n+1(n+1)p=E(1+B)1

09

Final Answer (Part c)

Hence, the required expression is,E(1+B)1=1(1p)n+1(n+1)p.

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