Stithscienceexchange Puzzlers

Don Hall was one of my mentors.  He began his teaching career in a one room school house in Rangely, Maine.  He talk all grade levels during his amazing career, including graduate students in college.  This is one of his puzzles I remember:


If a hen and a half can lay an egg and a half in a day and a half, how long does it take a dozen hens to lay a dozen eggs?