Question 507184
In a gambling game a man is paid $3 if he draws a jack or queen and $5 if he draws a king or ace from an ordinary deck of 52 playing cards. If he draws any other card, he looses. How much should he pay to play if the game is fair?
<pre>
Suppose he pays x dollars to play:

           X          P(X)      E(X)=X*P(X)
Draw    Winnings   Probability   Expection  
  J       3-x         {{{1/13}}}          {{{expr(1/13)(3-x)}}} 
  Q       3-x         {{{1/13}}}          {{{expr(1/13)(3-x)}}}
  K       5-x         {{{1/13}}}          {{{expr(1/13)(5-x)}}}
  A       5-x         {{{1/13}}}          {{{expr(1/13)(5-x)}}}
other      -x         {{{9/13}}}          {{{expr(9/13)(-x)}}}

{{{sum(E(X)) = expr(1/13)(3-x)+expr(1/13)(3-x)+expr(1/13)(5-x)+expr(1/13)(5-x)+expr(9/13)(-x))}}}

Set that = 0

{{{expr(1/13)(3-x)+expr(1/13)(3-x)+expr(1/13)(5-x)+expr(1/13)(5-x)+expr(9/13)(-x)=0}}}

Multiply through by 13

{{{(3-x)+(3-x)+(5-x)+(5-x)-9x=0}}}

{{{3-x+3-x+5-x+5-x-9x=0}}}

{{{16-13x=0}}}

{{{-13x=-16}}}

{{{x=16/13="$1.23"}}}{{{1/13}}}


Edwin</pre>