Numeracy makes for better investors

Many years ago, I read a book by John Allen Paulos, an American teacher of mathematics. Paulos recounted some examples from a test he conducted for potential employees of an organisation he was consulting with. One of the questions was whether if a quantity grows from 50 to 100, has it increased by 50%, 100%, or 200%? The answers that the candidates gave were all over the place, indicating that many of them were just guessing. It's notable that getting the answer correct requires no great competence in calculations - it's entirely a question of understanding the underlying concept. There was another question where the test takers were asked about the population of the United States, which was about 220 million at the time. This was not a multiple-choice question and the test-takers had to actually write down the answer. Perhaps half the test-takers got