SOLUTION: n one version of the game Keno, the house has a pot containing 80 balls, numbered 1 through 80. A player buys a ticket for $1 and marks one number on it (from 1 through 80). The
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Question 357978: n one version of the game Keno, the house has a pot containing 80 balls, numbered 1 through 80. A player buys a ticket for $1 and marks one number on it (from 1 through 80). The house then selects 20 of the 80 numbers at random. If the number selected by the player is among the 20 selected by the house (the management), the player is paid $3.20. Find the expected net winnings for this game.
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
The probability of catching exactly
spots when you have bet on
out of 80 spots is given by:
Where
is the number of combinations of
things taken
at a time and is calculated by
And the expected payout for a bet on
out of 80 spots is given by:
where
is the payout for catching
spots when you have bet on
out of 80 spots and
is the amount bet.
For your problem, you only have to count from 0 to 1, your amount bet is $1, and the payout for 1 out of 1 is $3.20, so:
Of course, since there is zero payout for not hitting the number, this reduces to:
Still, you are faced with what looks like a nasty bunch of arithmetic.
But because we know that
, this becomes:
And because we know from the definition of factorials
, we can write:
And finally:
This is actually a big payout. Most Vegas casinos get 25 cents from every dollar played.
John

My calculator said it, I believe it, that settles it
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