A problem by Anita Paul
Zara and John are both liars. They both lie on some specific days.
Zara lies of Fridays, Saturdays and Sundays. She speaks truth on all other days.
John lies on Tuesdays, Wednesdays and Thursdays. He speaks truth on all other days.
Can you tell that one day of the week when both of them will say "Tomorrow, I will lie."?