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re: Flip a coin 6 times. What are the odds for exactly 5 tails?

Posted on 8/31/23 at 6:52 am to
Posted by LordSaintly
Member since Dec 2005
38914 posts
Posted on 8/31/23 at 6:52 am to
You didn't say whether the coin is fair. I'll assume it is.

Use a binomial distribution with trials = 6, successes = 5, and p=0.5. The probability is 0.094, and the odds are 0.094 / 0.906.

Posted by Chucktown_Badger
The banks of the Ashley River
Member since May 2013
31138 posts
Posted on 8/31/23 at 8:17 am to
I think the odds for getting any particular distribution you want to pick are always going to be the same: 0.5^6
This post was edited on 8/31/23 at 8:18 am
Posted by HeadSlash
TEAM LIVE BADASS - St. GEORGE
Member since Aug 2006
49677 posts
Posted on 8/31/23 at 8:24 am to
7
Posted by Shanegolang
Denham Springs, La
Member since Sep 2015
3457 posts
Posted on 8/31/23 at 8:28 am to
Subtle "I have money" brag.
Posted by Ingeniero
Baton Rouge
Member since Dec 2013
18287 posts
Posted on 8/31/23 at 8:39 am to
quote:

I think the odds for getting any particular distribution you want to pick are always going to be the same: 0.5^6


Any single distribution, yes. But OP asked for exactly 5 tails. There are 6 ways to roll that:
quote:

HTTTTT
THTTTT
TTHTTT
TTTHTT
TTTTHT
TTTTTH

And 2^6=64 unique rolls

6/64=9.375% probability of exactly 5 tails

But he asked for the odds, so scenarios where it happens:scenarios where it doesn't.

(6/64)/(1-(6/64))
(6/64)/(58/64)
(6/58)=(3/29)
Like I said before, it's counterintuitive to write odds as a fraction in that way because it's too easily confused with probability. I'd write it as 29/3 or 29:3 if this was gambling, which is the same as 9.375% probability

ETA: the way I did 6/64 is the intuitive way, but for larger samples (say, flipping a coin 1000 times and wanting the probability of exactly 746 tails) you'd use the equation for binomial distribution. Unless you really like writing out permutations by hand
This post was edited on 8/31/23 at 8:53 am
Posted by Chucktown_Badger
The banks of the Ashley River
Member since May 2013
31138 posts
Posted on 8/31/23 at 8:46 am to
Yup, it just struck me and I was coming back in here to edit my post
Posted by Spasweezy
Unfortunately, Louisiana
Member since Jan 2014
6617 posts
Posted on 8/31/23 at 9:13 am to
The shoe is blue.
Posted by GumboPot
Member since Mar 2009
118835 posts
Posted on 8/31/23 at 9:19 am to
quote:

But he asked for the odds




That was on purpose but not as a gotcha. Until my son came to me with this problem from his LSU probability course I've always conflated probability with odds like most people. The two concepts are different as you have outlined.
Posted by Bestbank Tiger
Premium Member
Member since Jan 2005
71133 posts
Posted on 8/31/23 at 9:24 am to
quote:

Whatever the odds are, they are much higher than going to Vegas and consecutively betting 6 times on "Red" on the roulette wheel and winning 5 times. Amazingly the house has much greater odds of beating you 5 out of 6 times on a basically 50/50 bet. It's really uncanny.


It isn't a 50/50 bet. There are four green squares.
Posted by LordSaintly
Member since Dec 2005
38914 posts
Posted on 8/31/23 at 9:49 am to
quote:

0.5^6


That's the probability of six heads in a row which isn't what the OP needs.
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