# The true and false babies [duplicate]

There are two babies, the truth baby and the false baby. The truth baby will respond to any question with a true answer, and the false baby will respond to any question with a false answer. The babies share a language of either burping or farting. A burp or fart would mean yes and no, but you don't know which is which. You also do not know which is the truth baby and which the false baby.

You are to ask each baby a single yes-or-no question. Your goal is to discover whether or not the truth baby has hair. (You can't simply look at it to find out, you must only use knowledge that you gain from asking questions.)

## 1 Answer

A simple variation on the two guards problem.

Ask of one baby, "Are you the truth-teller?" Whichever response you get, you know that means yes, and therefore the other means no. Go to the remaining baby and ask, "Would the other baby say that the truth-teller has hair?" If the truth-teller does have hair, the truth-teller would say that the liar would lie and say no, and the liar would lie and say that the truth-teller would say no. It works the same way in reverse, so whichever answer you get for this, the reality is the opposite.