About 14 years ago I watched an episode of Millionaire where I saw a contestant get a question about how many gifts there were in the song about the 12 Days of Christmas. He guessed 78, as did I, but both of us were shocked to find out it was 364.
You're wondering how we both guessed 78: Simple, the first line in each verse (i.e. the partridge on the first day, turtle doves on the second, etc.).