- From the almanac (the only authority required), Chicago has a population of about 3 million people.
- Assume that an average family contains four members (Fermi was teaching in the 1930s when families were that large).
- Therefore the number of families in Chicago is about 750,000.
- If one in five families owns a piano, there will be 150,000 pianos in Chicago.
- If the average piano tuner serviced four pianos every day of the week for five days rested on weekends, and had a two week holiday during the summer, then in one year (52 weeks) he would service 1,000 pianos. 150,000/(4 x 5 x 50) = 150, so that there must be about 150 piano tuners in Chicago.
As an exercise, what is the simplest argument against the Young Earth Creationism - the theory that God created the world about 5,700 years ago? Most people now accept that God created the world (together with time and space, and the number system) more than 14 billion years ago. But why do they accept that? What is the simplest argument for the generally accepted age of the universe that you could write down on a credit card, and which you could explain to a 9 year old? You will find that this article, which is completely incomprehensible, is absolutely no use. I offer a prize of a £5 Waitrose voucher to the first decent reply to my challenge.