I cant remember clearly, but I dont think anyone in the class got it right. The logic was that every day and a half, a number of hens laid the same number of eggs, so each hen laid one egg every day and a half.
I recall a small boy challenging this, along the lines of: "That's wrong Mr Higgins. My Auntie Nelly has got a hen, and it lays an egg every day"
As usual, the teacher hit the roof.