statistical question

RoamingMadness · Post by **RoamingMadness** » Fri Sep 01, 2006 7:59 pm

Mikeyrat wrote:Probability, though, is 2/100 = (1-).02 = .98 , while 1/100 is .01 or .99. As you can see by doubling the number of chances doesn't double the "probability".

2/100 = .98
1/200 = .99

Thus the "probability" of playing one number is .01, and the "probability" of playing two numbers is .02

Now do you notice that .02 is exactly DOUBLE .01

Hence, regardless of how you swing it. It does "double" the probablity of it happening.

If you roll a 100 sided die about 10000 times, counting the number of times you hit 1. It will hit about 100 times. If you count the number of times it will hit about 1 or 2. It will happen about 200 times. All you did was add 1 more number. And just like adding one more ticket, your chances double.

Foams link explains not only this. But also nicely points out its a waste of money. Which is helpful i think.

Post by **Kadian** » Sat Sep 02, 2006 12:32 am

The conversion of odds to probability (source: Introduction to Business Statistics, Ronald M. Weiers)
"If the odds in favor of an event happening are A to B, or A:B, the probability being expressed is A/A+B."

The question is "are the odds doubled when you go from 1:100 to 2:100", to convert odds to probability.

For 1:100
A=1, B=100
1/1+100 = .00990099r or 9.9%

For 2:100
A=2, B=100
2/2+100 or 2/102= .0196 or 19.6%

.00990099r doubled is .01980198r, or 9.9% doubled is 19.8%. So we can conclude that the odds (converted into probability) is more than doubled by doubleing the first number.

Now the other question is "is 2:100 the same as 1:50" let's see.

For 1:50
A=1, B=50
1/1+50 or 2/51= .0196 or 19.6%, so it is the same as 2:100 odds.

Post by **Kadian** » Sat Sep 02, 2006 12:41 am

I have to agree with roam, I noticed also that .02 IS double of .01, and if you do 4, it is double and is .04.
As Styro showed at the end of that page is a form of the binomial probability distribution (also in my textbook) so take a close look at that, the "!" means that you have to take the number, say 5 for example, and do this 5x4x3x2x1, or 120.

RoamingMadness · Post by **RoamingMadness** » Sat Sep 02, 2006 2:31 am

Kadian wrote:"If the odds in favor of an event happening are A to B, or A:B, the probability being expressed is A/A+B."

Two things for the record. If anyone was confused. This formula is for things like raffles where the number of tickets sold, bases the odds. Not for things like Roulette, lottery, keno, or anything else which has fixed odds.

Secondly. That formula should be A/(A+B).

That is all.

Octa · Post by **Octa** » Sat Sep 02, 2006 9:18 am

I think it is safe to say that none of us here are on the verge of winning a Field's Medal.

Post by **Kadian** » Sat Sep 02, 2006 9:37 am

RoamingMadness wrote: Two things for the record. If anyone was confused. This formula is for things like raffles where the number of tickets sold, bases the odds. Not for things like Roulette, lottery, keno, or anything else which has fixed odds.

Maybe you're right, and for the record, I was just trying to add some real math from a textbook so we could use it to discuss, I was not trying to say that I know everything about it or have all the answers.

RoamingMadness wrote: Secondly. That formula should be A/(A+B).

I think it's obvious by my calculations that I was doing it that way.
2/2+100 or 2/102
But yes, if you want to be picky, it should have been written that way.

RoamingMadness · Post by **RoamingMadness** » Sat Sep 02, 2006 9:56 am

Kadian wrote:
RoamingMadness wrote: Two things for the record. If anyone was confused. This formula is for things like raffles where the number of tickets sold, bases the odds. Not for things like Roulette, lottery, keno, or anything else which has fixed odds.

Maybe you're right, and for the record, I was just trying to add some real math from a textbook so we could use it to discuss, I was not trying to say that I know everything about it or have all the answers.
RoamingMadness wrote: Secondly. That formula should be A/(A+B).
I think it's obvious by my calculations that I was doing it that way.
2/2+100 or 2/102
But yes, if you want to be picky, it should have been written that way.

I know that you knew that, otherwise the numbers would have been off. I was just saying it for anyone who was playing along at home.

Styrofoam · Post by **Styrofoam** » Sat Sep 02, 2006 11:34 am

Octa wrote:I think it is safe to say that none of us here are on the verge of winning a Field's Medal.

lol! Even the smartest mathmatitian didn't win it rofl.