程阳:Powerball Odds (1)
(2008-08-26 16:46:39)
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程阳:Powerball Odds (1)
How to Calculate the Probabilities for the
Powerball Lottery
(Updated for the 55 ball game)
If the only thing you are interested in is the probability (odds)
of winning the Powerball Jackpot, the Multi-State Lottery gives a
concise table at their web
site. We will give the same information here, but also show you
how these odds are calculated.
Game Rules
The numbers picked for the
prizes consist of 5 white balls picked at random from a drum that
holds 55 balls numbered from 1 to 55. The Powerball number is a
single ball that is picked from a second drum that has 42 numbers
ranging from 1 to 42. If the results of these random number
selections match one of the winning combinations on your lottery
ticket, then you win something. You can also buy a “Power Play
Multiplier” option – the size of which is determined by a random
spin of a “Multiplier Wheel” that has four 2’s, four 3’s, four 4’s,
and four 5’s.
In any combinatorics problem
where all possible outcomes are equally likely, the probability of
a successful outcome is determined by finding the number of
successful combinations, and then dividing by the total number of
all combinations. There are nine possible configurations that will
win something in the Powerball Lottery. For each of these, the
probability of winning equals the number of winning combinations
for that particular configuration divided by the total number of
ways the Powerball numbers can be picked.
Powerball Total Combinations
Since the total number of
combinations for Powerball numbers is used in all the calculations,
we will calculate it first. The number of ways 5 numbers can be
randomly selected from a field of 55 is: COMBIN(55,5) = 3,478,761.
(See the math notation
page or Help in Microsoft's Excel for more information on
“COMBIN”).
For each of these 3,478,761
combinations there are COMBIN(42,1) = 42 different ways to pick the
Powerball number. The total number of ways to pick the 6 numbers is
the product of these. Thus, the total number of equally likely
Powerball combinations is 3,478,761 x 42 = 146,107,962. We will use
this number for each of the following calculations.
Jackpot probability/odds (Payout
varies)
The number of ways the 5 numbers on your lottery ticket can match
the 5 white balls is COMBIN(5,5) = 1. The number of ways your
Powerball number can match the single Powerball number is:
COMBIN(1,1) = 1. The product of these is the number of ways you can
win the Jackpot: COMBIN(5,5) x COMBIN(1,1) = 1.
The probability of success is thus: 1/146,107,962 =
0.00000000684425. If you express this as “One chance in ???”, you
just divide “1” by the 0.00000000684425, which yields “One chance
in 146,107,962”.
Match all 5 white balls but not the Powerball
(Payout = $200,000)
The number of ways the 5 numbers on your lottery ticket can match
the 5 white balls is COMBIN(5,5) = 1. The number of ways your
Powerball number can match any of the 41 losing Powerball numbers
is: COMBIN(41,1) = 41. (Pick any of the 41 losers.) Thus there are
COMBIN(5,5) x COMBIN(41,1) = 41 possible combinations. The
probability for winning $200,000 is thus 41/146,107,962 =
0.000000280614 or “One chance in 3,563,608.83”.
Match 4 out of 5 white balls and match the
Powerball (Payout = $10,000)
The number of ways 4 of the 5 winning numbers on your lottery
ticket can match the 5 white balls is COMBIN(5,4) = 5. The number
of ways the losing white number on your ticket can match any of the
50 losing white numbers is COMBIN(50,1) = 50. The
number of ways your Powerball number can match the single Powerball
number is: COMBIN(1,1) = 1. The product of these is the number of
ways you can win this configuration: COMBIN(5,4)
x COMBIN(50,1) x COMBIN(1,1) = 250. The probability of success is
thus: 250/146,107,962 = 0.00000171106 or “One chance in
584,431.85”.
Match 4 out of 5 white balls but not match the
Powerball (Payout = $100)
The number of ways 4 of the 5 winning numbers on your lottery
ticket can match the 5 white balls is COMBIN(5,4) = 5. The number
of ways the losing white number on your ticket can match any of the
50 losing numbers is COMBIN(50,1) = 50. The
number of ways your Powerball number can miss matching the single
Powerball number is: COMBIN(41,1) = 41. The product of these is the
number of ways you can win this configuration:
COMBIN(5,4) x COMBIN(50,1) x COMBIN(41,1) = 10,250. The probability
of success is thus: 10,250/146,107,962 = 0.0000701536 or “One
chance in 14,254.44”.
Match 3 out of 5 white balls and match the
Powerball (Payout = $100)
The number of ways 3 of the 5 winning numbers on your lottery
ticket can match the 5 white balls is COMBIN(5,3) = 10. The number
of ways the 2 losing white numbers on your ticket can match any of
the 50 losing white numbers is COMBIN(50,2) =
1,225. The number of ways your Powerball number
can match the single Powerball number is: COMBIN(1,1) = 1. The
product of these is the number of ways you can win this
configuration: COMBIN(5,3) x COMBIN(50,2) x
COMBIN(1,1) = 12,250. The probability of success is thus:
12,250/146,107,962 = 0.0000838421 or “One chance in
11,927.18”.
Match 3 out of 5 white balls but not match the
Powerball (Payout = $7)
The number of ways 3 of the 5 winning numbers on your lottery
ticket can match the 5 white balls is COMBIN(5,3) = 10. The number
of ways the 2 losing white numbers on your ticket can match any of
the 50 losing numbers is COMBIN(50,2) = 1,225.
The number of ways your Powerball number can miss matching the
single Powerball number is: COMBIN(41,1) = 41. The product of these
is the number of ways you can win this
configuration: COMBIN(5,3) x COMBIN(44,2) x
COMBIN(41,1) = 502,250. The probability of success is thus:
502,250/146,107,962 = 0.003437527 or “One chance in 290.91”.
Match 2 out of 5 white balls and match the
Powerball (Payout = $7)
The number of ways 2 of the 5 winning numbers on your lottery
ticket can match the 5 white balls is COMBIN(5,2) = 10. The number
of ways the 3 losing white numbers on your ticket can match any of
the 50 losing white numbers is COMBIN(50,3) =
19,600. The number of ways your Powerball number
can match the single Powerball number is: COMBIN(1,1) = 1. The
product of these is the number of ways you can win this
configuration: COMBIN(5,2) x COMBIN(50,3) x
COMBIN(1,1) = 196,000. The probability of success is thus:
196,000/146,107,962 = 0.001341474 or “One chance in 745.45”.
Match 1 out of 5 white balls and match the
Powerball (Payout = $4)
The number of ways 1 of the 5 winning numbers on your lottery
ticket can match the 5 white balls is COMBIN(5,1) = 5. The number
of ways the 4 losing white numbers on your ticket can match any of
the 50 losing white numbers is COMBIN(50,4) =
230,300. The number of ways your Powerball number
can match the single Powerball number is: COMBIN(1,1) = 1. The
product of these is the number of ways you can win this
configuration: COMBIN(5,1) x COMBIN(50,4) x
COMBIN(1,1) = 1,151,500. The probability of success is thus:
1,151,500/146,107,962 = 0.007881158 or “One chance in
126.88”.
Match 0 out of 5 white balls and match the
Powerball (Payout = $3)
The number of ways 0 of the 5 winning numbers on your lottery
ticket can match the 5 white balls is COMBIN(5,0) = 1. The number
of ways the 5 losing white numbers on your ticket can match any of
the 50 losing white numbers is COMBIN(50,5) =
2,118,760. The number of ways your Powerball
number can match the single Powerball number is: COMBIN(1,1) = 1.
The product of these is the number of ways you can win this
configuration: COMBIN(5,0) x COMBIN(50,5) x
COMBIN(1,1) = 2,118,760. The probability of success is thus:
2,118,760/146,107,962 = 0.014501332 or “One chance in 68.96”.
Probability of winning something
If we add all the ways you can win something we get:
1 + 41 + 250 + 10,250 + 12,250 + 502,250 + 196,000 + 1,151,500 +
2,118,760 = 3,991,302 different ways of winning something. If we
divide this number by 146,107,962, we get .027317485 as a
probability of winning something. 1 divided by
0.027317485 yields “One chance in 36.61” of winning
something.
Corollary
You can get a close estimate
for the number of tickets that were in play for any given game by
multiplying the announced number of “winners” by the above 36.61.
Thus, if the lottery officials proclaim that a given lottery
drawing had 2 million “winners”, then there were about 2,000,000 x
36.61 ~= 73,220,000 tickets purchased that did not win the Jackpot.
Alternately, there were about 73,220,000 - 2,000,000 ~= 71,220,000
tickets that did not win anything.
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