A friend on twitter was posting various riddles, and I remembered one that my dad told me when I was a kid. Unfortunately, it was too long for Twitter, so I’m posting it here, just for fun.

Riddle me this:
You’re buying a house, and everything is set for a smooth closing. When you arrive at the closing table, there are two envelopes on the table. It turns out that the sellers were in a good mood because they had just won the lottery. They’re still feeling a little giddy about the whole thing, and decide to have a little fun with you.

Although the envelopes both look and weigh exactly the same, one envelope has all of the documents you are to sign just as planned. However, the other envelope has enough cash to pay for the house in full. Pick one envelope, and you’ll have a loan on the home just as you had planned. Pick the other, and you’ll own the home free and clear - right then and there.

The only two people who know which envelope is “the winner” - are the two sellers. No matter what question you ask - one of them is guaranteed to lie to you, and one of them is guaranteed to tell you the truth. Unfortunately, you have no way of knowing which one will lie and which one will tell the truth. You are also told that you are only allowed to ask them one question. (You must ask each of them the same question.)

If you are only allowed to ask them one question, what question will you ask in order to pick the envelope that will get your home paid off in full?