# The Two Identical Twins [closed]

There are 2 twins who think the same, look the same, sound the same, and act the same. The only difference is that 1 of them is male, 1 is female. Without asking the twins for their gender, how can you figure this out? You have a maximum of 2 questions.

• Does that also exclude implied gender questions like "Can you get pregnant?" Commented Oct 5, 2014 at 16:10
• Unless by “act the same” you mean that they’ll give the same answer to every question, the top two answers both seem fine. If that is what you mean, well… “can I have a blood sample”?
– Ry-
Commented Oct 6, 2014 at 6:53
• Does the term "twin" imply that there are no other siblings who where born at the same time? Commented Oct 6, 2014 at 9:55
• You can do it in zero questions - undress them. Commented Oct 6, 2014 at 17:15
• Do they always lie or always tell the truth? Or do they randomly lie? Commented Oct 6, 2014 at 17:16

## 2 Answers

If I asked your twin which gender you are, what would they tell me?

Even if they're both liars you'll get the right answer - as the one you're asking would lie about what the other would say, who would also lie.

For the people confused about this, in the world of riddles the person you're asking is an oracle who is generally omniscient (they know the answers to your questions), consistent (for a given question, they'll always answer the same way), and gives meaningful information.

It's also a common trope that when you have essentially a binary question to ask one of multiple oracles, they might be liars. Sometimes this is spelled out, like in the Knights and Knaves puzzle many are familiar with in the door riddle from the movie Labyrinth. Sometimes, as in this question, spelling it out would basically give away the answer.

A big clue here was that they "act the same" - which is otherwise out of place.

If the oracle is inconsistent (or doesn't know the answers in the first place) you can't get useful information at all - and you don't have a riddle.

What if they answer with gibberish?

Then you can't get meaningful information and don't have a riddle.

What if they answer inconsistently, lying only sometimes?

Then you can't get meaningful information and don't have a riddle.

What if they just answer "female" to every question?

Then you can't get meaningful information and don't have a riddle.

...

and so on.

So probably the biggest clue here is that it is in fact a riddle therefore you can throw the useless absurdities right out.

• The puzzle doesn’t say anything about lying. Even if they can lie and will act exactly the same, they may still give different answers to the questions of “which gender are you?” and your solution.
– Ry-
Commented Oct 6, 2014 at 7:05
• Finally someone who realized they might lie! +1 for only 1 question and not asking "Is the sky blue?" XD Commented Oct 6, 2014 at 18:08
• But what if they sometimes lie and sometimes tell the truth (that is to say, normal people)? This answer won't work then. Commented Oct 6, 2014 at 19:22
• They could just answer questions randomly for any reason. As you did not specify rules for truth tellers vs. liars there is no reason for this answer to make sense. If the boy, for instance, pretends to be a girl and the girl goes along with it, this answer does not work. Commented Oct 6, 2014 at 20:07
• For all we know, they could just both answer "foobar" to any question, every time!!! Commented Oct 13, 2014 at 9:42

Ask one: "Do you have a twin brother?" If answer is "yes", so this twin is female, otherwise this twin is male.

• I agree - well done :-) Commented Oct 5, 2014 at 18:27
• You're still missing something. Commented Oct 5, 2014 at 18:54
• @warspyking What am I missing? The question "do you have a (twin) brother?" seems to solve the problem... Commented Oct 5, 2014 at 19:02
• There's a specific reason you require 2 questions. They act alike. Remember that. Commented Oct 5, 2014 at 19:21
• @warspyking In what situation could this not give the correct answer? Commented Oct 6, 2014 at 3:03