I think it's actually been 2.5 years, this time.

[theweaselking]

It's That Time Of Year Again!

You run a zoo! Your head cloning scientist says she has two new baby velociraptors to show you. You fire her immediately for CLONING VELOCIRAPTORS, but you're still stuck with a few million dollars worth of baby animal that you can't necessarily afford to trash out of hand.

"Well", you think, "at least if they're all male, they can't breed with my *existing* population of 100%-male no-frog-DNA screw-you-Crichton velociraptors. Exactly 50% of all cloned velociraptor babies are male! Maybe I can keep them."

So you call your *new* head cloning scientist and ask *her* if at least one of the babies is male. She is briefly confused about the nature of your query, and then she has to bone up (no pun intended) on sex determination of infant cloned dinosaurs, but then she comes back and says "Yes! One of the babies is male!"

While this is technically the question you asked, this is not the answer you *wanted*. So, facing the loss of millions and losing your temper, you thank her and hang up so you can think.

And so, we reach your question: What are the odds that the second velociraptor is also male?

[EDIT: Your question was "is at least one male?". Her answer is "Yes! At least one is male!". This is not a trick based on the wording from your second-best cloning scientist.]

[EDIT2: Is is not a wording-based trick of any sort. You have two babies, each with a 50% chance of being male and a 50% chance of being female. One of the babies is male. What are the odds that the other baby is also male?]

Comments

[dreamshade.livejournal.com]

I'm not even going to answer this one because this one is old, old, old, old (at least, in forms that don't deal with velociraptors), and anyone who gets it wrong is very new to math-based brain teasers.

[theweaselking.livejournal.com]

The raptors and snark are there to make it harder to Google.

[pope-guilty.livejournal.com]

As I've said, I'm fairly ignorant of probability, and my ignorant guess would be 50%. The odds of throwing heads or tail on a single coin throw are 50% regardless of previous throws, and so it seems to me that knowing that at least one of the raptors is male doesn't have any bearing on whether the sex-unknown raptor is male or female. So I'm saying 50%, with no particular confidence and based on nothing more than analogizing from another case in which you know one outcome but not another.

[dreamshade.livejournal.com]

Fair enough~

[scifantasy.livejournal.com]

33%.

There are four scenarios, as follows:

Velociraptor Baby #1 (henceforth, VB1) is female, Velociraptor Baby #2 (henceforth, VB2) is female.
VB1 is male, VB2 is female.
VB1 is female, VB2 is male.
VB1 is male, VB2 is male.

From the data we have, we know the first scenario is impossible.

Therefore, the question becomes, of the three scenarios, how many have two males? Answer: one. Hence, 1/3, or 33%.

[dreamshade.livejournal.com]

*bzzzzzzzzzzzzt* Thank you for playing our game! We have some lovely parting gifts for you~

[pope-guilty.livejournal.com]

*shrug*

I wouldn't even have said anything if John hadn't told me to.

[cuddlycthulhu.livejournal.com]

33%?

[theweaselking.livejournal.com]

I will note, for the record, that the last time I asked this question, you got it wrong.

Are you *sure*?

[dreamshade.livejournal.com]

Yeah, sorry, I'm acting like a dick because I got myself started on the first post. I probably got this wrong the first time I was asked it (though I don't quite remember when that was).

[scifantasy.livejournal.com]

Are you *sure*?

No, but I really don't care all that much anyway.

[pope-guilty.livejournal.com]

It does occur to me that she said "One of the babies is male", not "at least one of the babies is male" so possibly the answer is that one's male and one's female or intersex but honestly this sort of thing is so ludicrously counterintuitive that it's hard to feel bad about being wrong.

Then again, I somehow doubt that the point of the question is to laugh at people for accepting the premise.

[harald387.livejournal.com]

This isn't the first time I've been asked it.

This also isn't the first time I've gotten it wrong.

And it isn't the first time I've felt like an idiot for not being able to figure it out.

[cheshire-bitten.livejournal.com]

Well I am amused.

[kafziel.livejournal.com]

Well, that depends. If this is a rephrased Monty Hall problem, then it's 1/3rd. If she only tested one and that one turned out male, and she didn't test the other at all, then 50%.

[pope-guilty.livejournal.com]

Oh, Angelspit. :D

[theweaselking.livejournal.com]

Have you not seen any of the Jurassic Park movies?

Cloning raptors was a mistake the first time, but you can't just destroy millions of dollars of R&D and immensely valuable live products. So you keep them and you hope your liability insurance accepts your disclaimers when the raptors get out, and you definitely don't let them breed.

And then your head scientist comes to you with "Hey, look, more raptors! I've made them BETTER!" Oh, fuck yes, you fire that person.

[theweaselking.livejournal.com]

Your answer is wrong!

(I'm not saying how, yet)

[cosmiccat.livejournal.com]

Okay, going to bite, even though these things are invariably Schmuck Bait:

0%. Exactly 50% of all cloned velociraptor babies are male. This is because there are only two cloned velociraptor babies in existence, they are in your lab, and only one is male.

[spawnofweevil.livejournal.com]

If the velociraptor babies were both cloned from the same source, I'd think they'd both be male, what with being clones? Or are they clones of different velociraptors...?

[kafziel.livejournal.com]

Or maybe by saying "One of them is male." there is an implicit "and only one" which she didn't feel the need to say. Like how if you'd given her ten with 1 female, she'd say "9 of them are male." In which case the probability is 0, because you know that the other one is not.

There's really not enough information to make a judgment as to probability here. I blame you, for choosing to write this in English.

[theweaselking.livejournal.com]

I've edited the question to compensate. Short version: It's not a trick question.

[blake-reitz.livejournal.com]

The answer is NATURE FINDS A WAY!

[theweaselking.livejournal.com]

Hah!

Great answer, but not what I intended. 50% of cloned velociraptor babies are male, by virtue of each cloned velociraptor having a 50/50 chance of being male/female.

[theweaselking.livejournal.com]

Haven't you seen Jurassic Park?

(More seriously: 50% of the output of your cloning effort are male, 50% female. IT IS MAGICAL.)