### Delanceyplace: Things You Didn't Know You Didn't Know

In today's selection -- though the average person is more likely to drop dead within one hour of purchasing a lottery ticket than to win the lottery, here are two strategies for you to consider, suggests **John D Barrow**.

The UK National Lottery has a simple structure. You pay £1 to select six different

numbers from the list 1, 2, 3, . . . , 48, 49. You win a prize if at least three

of the numbers on your ticket match those on six different balls selected by a

machine that is designed to make random choices from the 49 numbered balls. Once

drawn, the balls are not returned to the machine. The more numbers you match, the

bigger the prize you win. Match all six and you will share the jackpot with any

others who also share the same six matching numbers. In addition to the six drawn

balls, an extra one is drawn and called the 'Bonus Ball'. This affects only those

players who have matched five of the six numbers already drawn. If they also match

the Bonus Ball then they get a larger prize than those who matched only the other

five numbers.

What are your chances of picking six numbers from the 49 possibilities correctly,

assuming that the machine picks winning numbers at random? The drawing of each ball

is an independent event that has no effect on the next drawing, aside from reducing

the number of balls to be chosen from. The chance of getting the first of the 6

winning numbers from the 49 is therefore just the fraction 6/49. The chance of picking

the next of the remaining 5 from the 48 balls that remain is 5/48. The chance of

picking the next of the remaining 4 from the 47 balls that remain is 4/47. And

so on, the remaining three probabilities being 3/46, 2/45 and 1 /44. So the probability

that you pick them all independently and share the jackpot is:

6/49 X 5/48 x 4/47 x 3/46 x 2/45 X 1/44 = 720/10068347520

If you divide this out you get the odds as 1 in 13,983,816 -- that's about one

chance in 13.9 million. If you want to match 5 numbers plus the Bonus Ball, then

the odds are 6 times smaller, and your chance of sharing the prize is 1 in 13,983,816/6

or 1 in 2,330,636.

Let's take the collection of all the possible draws -- all 13,983,816 of them --

and ask how many of them will result in 5, or 4, or 3, or 2, or 1, or zero numbers

being chosen correctly. There are just 258 of them that get 5 numbers correct, but

6 of them win the Bonus Ball prize, so that leaves 252; 13,545 of them get 4 balls

correct, 246,820 of them that get 3 balls correct, 1,851,150 of them that get 2

balls correct, 5,775,588 of them get just 1 ball correct, and 6,096,454 of them

get none of them correct. So to get the odds for you to get, say, 5 numbers correct

you just divide the number of ways it can happen by the total number of possible

combinations, i.e. 252/13,983,816, which means odds of 1 in 55,491 if you buy one

lottery ticket. For matching 4 balls the odds are 1 in 1,032; for matching 3 balls

they are 1 in 57. The number of the 13,983,816 outcomes that win a prize is 1 +

258 + 13,545 + 246,820 = 260,624 and so the odds of winning any prize when you buy

a single ticket are 1 in 13,983,816/260,624, that is about 1 in 54. Buy a ticket

a week with an extra one on your birthday and at Christmas and you have an evens

chance of winning something.

This arithmetic is not very encouraging. Statistician John Haigh points out that

the average person is more likely to drop dead within one hour of purchasing a ticket

than to win the jackpot. Although it is true that if you don't buy a ticket you

will certainly not win, what if you buy lots of tickets?

The only way to be sure of winning a lottery is to buy all the tickets. There have

been several attempts to use such a strategy in different lotteries around the world.

If no jackpot is won in the draw, then usually the unwon prize is rolled over to

the following week to create a super-jackpot. In such situations it might be attractive

to try to buy almost all the tickets. This is quite legal! The Virginia State Lottery

in the USA is like the UK Lottery except the six winning numbers are chosen from

only 44 balls, so there are 7,059,052 possible outcomes. When the jackpot had rolled

over to $27 million, Australian gambler Peter Mandral set in operation a well-oiled

ticket buying and printing operation that managed to buy 90% of the tickets (a failure

by some of his team was responsible for the worrying gap of 10%). He won the rollover

jackpot and went home with a healthy profit on his $10 million outlay on tickets

and payments to his ticket-buying 'workers'.

**Author: John D. Barrow
Title: 100 Essential Things You Didn't Know You Didn't Know
Publisher: W.W. Norton & Company
Date: Copyright 2008 by John D. Barrow
Pages: 152-154**

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