Tomorrow you will meet three sisters, and be married to one of them. The eldest always tells the truth, the youngest always lies. The middle sister lies or tells the truth at random. Knowing this, you would like to marry the either the eldest or the youngest—so you'll know where you stand.
Conscious to their own futures, the sisters conspire to visit you the night before. Everyone gets on really well. They are Abigail, Eleanor and Lucy. You're too polite to guess their ages. As they're about to leave, Abigail draws you aside and says 'since we might be married tomorrow, is there anything you'd like to ask?'. From the look in her eyes, you understand it should be a yes-no question. To achieve your aim, what do you ask?
Needless to say, the sisters know each others' ages.
It might help to solve this simpler problem first Two doors with two guards - one lies, one tells the truth