A group of blondes walked into a bar chanting "51 days! 51 days!" They ordered a bottle of champagne and sat at a big table.

Later more blondes came in and they joined in chanting "51 days! 51 days!"

The bartender asked: "Why are you chanting 51 days?"

They said, "Well, the ten of us put this puzzle together and the box says 2-4 years, but we managed to do it in 51 days!"