d2jsp
Log InRegister
d2jsp Forums > Off-Topic > General Chat > Homework Help > Anyone Good At Math
Prev12
Add Reply New Topic New Poll
Member
Posts: 21,893
Joined: Mar 27 2009
Gold: 12,408.00
Nov 18 2014 12:45am
Quote (Uguu @ Nov 18 2014 12:43am)
there's 2 players.
50% chance to win and lose here brah
since there's 2 choice for who wins


You're wrong. There's a large statistical advantage to rolling first if you roll high.
Member
Posts: 1,995
Joined: Jun 28 2006
Gold: 7.41
Nov 18 2014 01:18am
Quote (Uguu @ Nov 18 2014 01:43am)
there's 2 players.
50% chance to win and lose here brah
since there's 2 choice for who wins


You roll a die. What's the probability that if I roll the same die, I will roll higher than you?

By your logic, its 50%. Because I either roll higher than you or I don't.

That is however absurd. Because it can't possibly be 50%. You have a win condition from the start. Of an N sided die, if you rolled N, then I can't possibly beat it. I have a 1/N chance of losing before I even roll. It will always be lower than 50%.

P(first > second) + P(first < second) + P(first = second) = 1

P(first > second) = P(first < second), due to the principle of symmetry
P(first = second) = 1/N

Therefore

P(second > first) + P(second < first) + 1/N = 1
P(second > first) + P(second > first) + 1/N = 1
2(P(second > first) = 1 - (1/N)

P(second > first) = [ 1 - (1/N) ] / 2

lim N->+infinity f(N) = [1 - (1/N)] / 2 = 1/2

This means it will NEVER be 50%. So you will always have an advantage. Going first. Now extrapolate that to you trying to beat theprevious roll each time as the subset of win rolls decreases as the number of rolls increases. This means each time you roll the dice you decrease your chance of winning. In this case the player who rolls second has a disadvantage, because he doesn't even need to roll the die to lose. All that he needs to loseis for player 1 to roll the highest value on his first roll, and he will win, because there is no way player 2 can beat that roll. Therefore, the person who rolls the dice the least has the greater probability of winning. But it is not 50%, because player 1 can win from his first roll.

This post was edited by Minkomonster on Nov 18 2014 01:25am
Member
Posts: 16,662
Joined: Nov 24 2007
Gold: 15,245.00
Trader: Trusted
Nov 18 2014 06:12pm
Probability for the first player to win is :

1 - ( 1 - 1/N ) ^ N

As N tends to infinity, this probability tends to 1 - exp(-1), that is approximately 63.2%.
Member
Posts: 1,995
Joined: Jun 28 2006
Gold: 7.41
Nov 18 2014 06:22pm
Quote (feanur @ Nov 18 2014 07:12pm)
Probability for the first player to win is :

1 - ( 1 - 1/N ) ^ N

As N tends to infinity, this probability tends to 1 - exp(-1), that is approximately 63.2%.


I am curious if you are Rainman, read the problem, and instantly knew the answer, or just didn't bother reading the rest of the thread to see that the article you found when you googled the question was already linked previously (by me)

Here, I will post it again:

http://cr4.globalspec.com/blogentry/21768/Roll-of-the-Dice-Newsletter-Challenge-January-2013

The point was to help the OP understand the math behind it. Not just tell him the answer in a ploy to make yourself look smart...
Member
Posts: 16,662
Joined: Nov 24 2007
Gold: 15,245.00
Trader: Trusted
Nov 18 2014 07:11pm
Quote (Minkomonster @ Nov 19 2014 01:22am)
I am curious if you are Rainman, read the problem, and instantly knew the answer, or just didn't bother reading the rest of the thread to see that the article you found when you googled the question was already linked previously (by me)

Here, I will post it again:

http://cr4.globalspec.com/blogentry/21768/Roll-of-the-Dice-Newsletter-Challenge-January-2013

The point was to help the OP understand the math behind it. Not just tell him the answer in a ploy to make yourself look smart...


Didn't see your previous link.
Sorry for my useless post then...
Member
Posts: 7,721
Joined: Oct 11 2008
Gold: 304.00
Nov 18 2014 07:39pm
Quote (feanur @ Nov 18 2014 07:11pm)
Didn't see your previous link.
Sorry for my useless post then...


:cry:
Go Back To Homework Help Topic List
Prev12
Add Reply New Topic New Poll