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Poll: A little math problem


What is the probalbility the other one is male?
0%
1.1% (7)
1.1% (7)
25%
5.6% (35)
5.6% (35)
33%
18.7% (117)
18.7% (117)
50%
63.8% (399)
63.8% (399)
66%
3.7% (23)
3.7% (23)
75%
3.5% (22)
3.5% (22)
100%
3.5% (22)
3.5% (22)
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Copy Clerk
Posts: 56
Joined: 6 Apr 2008

I was looking around on the internet, and I found something about Marilyn vos Savant. When I was reading about it I saw an interesting math problem. This was taken directly from Wikipedia, so I'm not certain about its accuracy in wording:

A shopkeeper says she has two new baby beagles to show you, but she doesn't know whether they're male, female, or a pair. You tell her that you want only a male, and she telephones the fellow who's giving them a bath. "Is at least one a male?" she asks him. "Yes!" she informs you with a smile. What is the probability that the other one is a male?

Please answer the poll before reading on.

I think Vos Savant said that it was a 1/3 chance, although the Wikipedia article wasn't very clear about it. However, I though it was interesting, and since this is seems to be a smart forum, I thought I'd ask it here.

Gone Gonzo
Posts: 2381
Joined: 6 Mar 2008

50% surely...?

Unless I'm missing something.

BANNED
Posts: 2994
Joined: 16 Aug 2008

No offfence but this thread is kinda stupid, and further more it's also pointless.

But whatever. I'm guessing 50%

Copy Clerk
Posts: 91
Joined: 19 Jun 2008

well, if their is only 2 beagles, we know one is a male, then thier is a 50/50 chance of the other being male or female....

Infamous Scribbler
Posts: 601
Joined: 20 Aug 2008

Does it matter what gender the other dog is?

Gone Gonzo
Posts: 3740
Joined: 18 Dec 2007

The chance that both dogs are male is 25%. Flip two coins, whats the chance of both being heads or both being tales? 25% with a 50% that one will be heads one will be tails.

The same thing applies here. I think. I might have read the question wrong.

Gone Gonzo
Posts: 1449
Joined: 16 May 2008

Okay. I feel stupid, but the 75% was jumping out at me.

Just a little flag going up in my brain somewhere. Either that, or early onset dementia.

Press Junketeer
Posts: 434
Joined: 10 Sep 2008

basically you're saying forget the dog we know is male, what's the other one? thusly it's 50/50 it can be male or it can be female.

Gone Gonzo
Posts: 1360
Joined: 21 May 2008

Should we factor in the chance that it could be a hermaphrodite?

Gone Gonzo
Posts: 1306
Joined: 17 Jun 2008

It's a pretty basic math problem unless you're supposed to factor in what GhostOfSin suggested. Then it's just trying to be tricky.

Copy Clerk
Posts: 120
Joined: 28 Sep 2008

75% works because we know one is male and the chance the other is male is half of that (1\2 of 25% + 50% = 75%)

I thought about this way too much.

Gone Gonzo
Posts: 1306
Joined: 17 Jun 2008

ObnoxiousTwat:
75% works because we know one is male and the chance the other is male is half of that (1\2 of 25% + 50% = 75%)

I thought about this way too much.

No, it would be 50% because it's a separate beagle, the other one being male would have no effect on it.

Gone Gonzo
Posts: 3740
Joined: 18 Dec 2007

ObnoxiousTwat:
75% works because we know one is male and the chance the other is male is half of that (1\2 of 25% + 50% = 75%)

I thought about this way too much.

Thats not the way probability works.

To find the probability of two things you must multiply them. The chance of one dog being male is 50% or 1/2.

1/2 is 0.5. 0.5 times 0.5 is 0.25 or 25%

The probability of both dogs being males is 25%. However looking at the question it appears to be asking what the chance of one dog being male is, which is 50%. It's a strange question that can interpreted differently.

Gone Gonzo
Posts: 2146
Joined: 7 Sep 2008

TheGhostOfSin:
Should we factor in the chance that it could be a hermaphrodite?

You just made my day, GhostOfSin- heck, you just made my week.

On the Record
Posts: 5136
Joined: 3 Mar 2008

50%.

Okay, factor in that it's a 100% chance that one of two is that it's female, and that the question asks what the other one will be, not regarding the male one.

It has to be 50%, because no matter what, there's an even chance of being male or female.

BASIC MATHS, PEOPLE: Read the question. They throw in Red Herrings on purpose.

Anonymous Source
Posts: 5
Joined: 12 Oct 2008

Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

Of these three possible outcomes, only one of them results in the second beagle being male.
Thats where the 33% comes from...
That's the logic behind the problem, however there's also the idea of independent events... the mind boggles.

On the Record
Posts: 6207
Joined: 10 Mar 2008

TheGhostOfSin:
Should we factor in the chance that it could be a hermaphrodite?

That's exactly what I was thinking after I finished reading the question...

But it's 50%, we know one dog's a male and they're asking what's the probability of the other being male. It's not asking for the possibility of a pair or not, just if the other is male or not.

50%

I just know there's something sinister behind this.

Copy Clerk
Posts: 120
Joined: 28 Sep 2008

Damn you math!! Even outside of school you make me look stupid.

Gone Gonzo
Posts: 1449
Joined: 16 May 2008

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

Of these three possible outcomes, only one of them results in the second beagle being male.
Thats where the 33% comes from...
That's the logic behind the problem, however there's also the idea of independent events... the mind boggles.

Never thought to use the Monty Hall problem for this. Nice.

Pulitzer Laureate
Posts: 785
Joined: 12 Aug 2008

50%: It's either a male or its something else.

Red Guard
Posts: 4892
Joined: 14 Oct 2007

Thing is, the gender of the second has no apparent relation to the gender of the first unless you factor in a whole shit load of biological variables which I don't really care to. As such, the two are as mutually exclusive as one coin-flip from the next. (Keep in mind that -any- series of coin results is as unlikely as any other.)

So I'll say 50%.

Gone Gonzo
Posts: 1011
Joined: 1 Dec 2007

Fire Daemon:

The probability of both dogs being males is 25%. However looking at the question it appears to be asking what the chance of one dog being male is, which is 50%. It's a strange question that can interpreted differently.

Not really.

dirtface:

Male Female
Female Male

This is the same thing

Gone Gonzo
Posts: 2146
Joined: 7 Sep 2008

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

Of these three possible outcomes, only one of them results in the second beagle being male.
Thats where the 33% comes from...
That's the logic behind the problem, however there's also the idea of independent events... the mind boggles.

This.

Then again, I don't remember very much about probability and the last time I studied that subject was 5 years ago.

On the Record
Posts: 7316
Joined: 23 Dec 2007

Yay Probability!

If you flip a coin and it comes up Heads 7/20 tosses, what are the chances the 21st toss will be Heads again?

Gone Gonzo
Posts: 1011
Joined: 1 Dec 2007

-deleted (not worth it)

Gone Gonzo
Posts: 1306
Joined: 17 Jun 2008

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

Of these three possible outcomes, only one of them results in the second beagle being male.
Thats where the 33% comes from...
That's the logic behind the problem, however there's also the idea of independent events... the mind boggles.

So is this thing right or were the rest of us right?

On the Record
Posts: 5896
Joined: 7 Mar 2008

based on the question stated in the pole it's 50% the other one is male

simply because you can disregard anything about the other dog, the lady is unsure if it's male or female but one is definitely male. so this means the other dog has a 50% chance of being male or female irregardless of the sex of the other dog

Gone Gonzo
Posts: 1374
Joined: 12 Sep 2007

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

Of these three possible outcomes, only one of them results in the second beagle being male.
Thats where the 33% comes from...
That's the logic behind the problem, however there's also the idea of independent events... the mind boggles.

Give this person a banana. The two beagles are already selected as part of a set; thus the 33%. If you selected one beagle, discovered it was male, then selected another beagle, the chance would be 50%. But if you select them two at a time and identify one as male, you remove the chance that both are female before the second chance.

Copy Clerk
Posts: 56
Joined: 6 Apr 2008

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

Of these three possible outcomes, only one of them results in the second beagle being male.
Thats where the 33% comes from...
That's the logic behind the problem, however there's also the idea of independent events... the mind boggles.

Well, this is actually why I posted this topic. I think that this is the mathematically proven solution, atleast according to Wikipedia. However, if you think about the problem as the person randomly grabbed one and it happened to be male, instead of looking at both and then replying, I think the answer is actually 50%. This answer seems right to me because if they just randomly grab one, there's a 50% chance that he would have grabbed a male in one of the two m/f pairs, and a 100% chance in the m/m pair. So, at least to my tired brain, there's a 50% chance that the male is from the m/m pair and a 50% from the m/f pair, therefore a 50% of the other being male. That seemed to be vaguely like the Bertrand's box paradox.

Press Junketeer
Posts: 434
Joined: 10 Sep 2008

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

fixed: that says the same as the one above it so it's irrelevant
we know that the first is male so it would look like this
male/ male
male/female

Gone Gonzo
Posts: 1306
Joined: 17 Jun 2008

werepossum:

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

Of these three possible outcomes, only one of them results in the second beagle being male.
Thats where the 33% comes from...
That's the logic behind the problem, however there's also the idea of independent events... the mind boggles.

Give this person a banana. The two beagles are already selected as part of a set; thus the 33%. If you selected one beagle, discovered it was male, then selected another beagle, the chance would be 50%. But if you select them two at a time and identify one as male, you remove the chance that both are female before the second chance.

But the gender of the second one isn't dependent on the first one. It's still 50% right?

Gone Gonzo
Posts: 2146
Joined: 7 Sep 2008

(ZHU) Michael:

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

fixed: that says the same as the one above it so it's irrelevant

Ah, but there's a reason it was like that- it was the order.

Anonymous Source
Posts: 5
Joined: 12 Oct 2008

Shivari:

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

Of these three possible outcomes, only one of them results in the second beagle being male.
Thats where the 33% comes from...
That's the logic behind the problem, however there's also the idea of independent events... the mind boggles.

So is this thing right or were the rest of us right?

... The wikipedia article states its 1/3, i was just explaining it.
For the other guy who said that male female was the same as female male - you're sortof correct, but not really. they are different cases that can be grouped...

Press Junketeer
Posts: 434
Joined: 10 Sep 2008

jamanticus:

(ZHU) Michael:

dirtface:
Ok this is like the monty hall problem.
If atleast one is male, you have three possible situations
Beagle1 Beagle 2
Male Male
Male Female
Female Male

fixed: that says the same as the one above it so it's irrelevant

Ah, but there's a reason it was like that- it was the order.

I came back for three mins. after leaving to have fun so im not getting into this cirle logic again

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