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What is the chance of losing a game where you have a 50% of winning each round, 5 rounds in a row?

PostPosted:Tue Dec 07, 2004 3:47 pm
by Flip
<div style='font: 10pt Tahoma; text-align: left; '>I ask because of this, i recently (for fun) started a sports gambling account on some betting website where i could put 5-10 dollars down on a football game. It has been fun and makes watching the games pretty exciting even when we are only talking about 5 bucks. For the last few week i've turned my 20 dollar initial deposit into 30 ^_^

Today, i noticed on the site that they also have a video craps game that lets you bet with your money. When you bet on the pass line, winning at craps is basicaly 50%, or maybe more like 47,48% since the house always has a slight advatange. Anyways, my system has been to put 1 dollar on the pass line, if i lose i'll put $2, if i lose that i'll put $4, then $8 then $16. That means i would have to lose 5 in a row to lose all my money, but if at any time i win one of those i have, essentially, won $1 to my total and i start back over at betting $1. So far, i've creeped up to $40, this system really seems to works. In fact, i havent even gotten to the 5th game yet before starting over at $1, so the most in a row i have lost so far is 3 before i win, increase my total by $1 and start back over.

This leads me to believe that is someone started with say $1,023 to where they could double their bets for 10 times, would they ever lose? How can you possibly lose a game 10 times in a row when you have a 50% chance of winning? If that is the case then you could creep that $1,000 up slowly by a dollar for an unlimited amount of times. It would take a while, but you could win a few hundred eventually, i think.

It has been looking like this:

started with: 30
bet 1: lose: 29
bet 2: lose: 27
bet 4: win: 31

bet 1: win: 32

bet 1: lose: 31
bet 2: win: 33

bet 1: lose: 32
bet 2: lose: 30
bet 4: win: 34

etc...

I've cracked vegas! ^_^</div>

found the answer...

PostPosted:Tue Dec 07, 2004 4:00 pm
by Flip
<div style='font: 10pt Tahoma; text-align: left; '>the probability is (1/2)^5 or 1/32, guess i should stop soon.</div>

If you've a lot more money than the house, then this method is sure to win.

PostPosted:Tue Dec 07, 2004 5:03 pm
by Don
<div style='font: 12pt ; text-align: left; '>Unfortunately, that is rarely the case.

The chance of losing 5 in a row is 1/32, but losing 5 in a row once will cost you $32, so you win $31 on the other 31 times you didn't lose 5 in a row, but you get set back to 0 when you do lose.</div>

PostPosted:Tue Dec 07, 2004 5:10 pm
by Kupek
<div style='font: 10pt verdana; text-align: left; padding: 0% 10% 0% 10%; '>If you have a lot more money than the house, then you really don't need to gamble.</div>

PostPosted:Tue Dec 07, 2004 9:34 pm
by ManaMan
<div style='font: 12pt Arial; text-align: left; '>.5*.5*.5*.5*.5=1/32, roughly 3%.</div>

Well, somehow i've managed to crawl this total up from the original 30 to 55 now.  There have been some close calls, though.  Gambling is fun, when you win.  I'd be pissed as hell if i lost some of those close ones.  Note to self : I n

PostPosted:Tue Dec 07, 2004 9:59 pm
by Flip
<div style='font: 10pt Tahoma; text-align: left; '>Who woulda thought this would be a softspot for me, maybe its just so fun because i've never really gambled before and its new.</div>

PostPosted:Wed Dec 08, 2004 12:27 am
by SineSwiper
<div style='font: 10pt "EngraversGothic BT", "Copperplate Gothic Light", "Century Gothic"; text-align: left; '>Stop after 16*5 rounds. That would give you roughly a 50/50 chance of winning a lot of money.</div>

PostPosted:Thu Dec 09, 2004 8:29 pm
by Don
<div style='font: 12pt ; text-align: left; '>Might as well bet a lot of money on the first round, that's also 50/50 of winning a lot of money.</div>