There's a catch. The questions have been devised by famed Princeton mathematics professor John H. Conway and range in difficulty from high school to PhD level.

Want to earn 3.14 years of free pizza from Pizza Hut ? All you have to do is answer three math questions.

The math contest kicked off Monday, known to math fans as National Pi Day because it mimics the first three digits of the mathematical constant pi. (3.14...)

Pizza Hut distributed the questions at 8 am ET via its website and will award three winners, one for each question.

Assuming, that is, that all of the problems are solved. A spokeswoman for Pizza Hut said that even the pizza chain doesn't know the answer to the hardest question. It is a "closely guarded secret" held by Conway, who will personally review any submissions for his tricky math problem.



Hardest Question: My key-rings are metal circles of diameter about two inches. They are all linked together in a strange jumble, so that try as I might, I can't tell any pair from any other pair. However, I can tell some triple from other triples, even though I've never been able to distinguish left from right. What are the possible numbers of key-rings in this jumble?



"Pi may be irrational, but free pizza is anything but," Conway, an award winning mathematician, said in a statement. "I'm eager to challenge America with these problems and find the next great pizza-loving mathematician that can solve them."



The pizza chain estimates that the 3.14 years of free pizza prize is worth about $1,600 in gift cards.

Of course, Pizza Hut isn't the only restaurant celebrating National Pi Day: