1. The number of pages haven't been adjusted for the size of the yellow pages and hence the size of the cities. (These same researchers found that personal bankruptcy rates tend to be higher in large cities than in smaller ones.) Also, the selection of 7 cities for one group and 5 for the other sounds like data mining. Perhaps most importantly, the causation may run the other way around: cities with lots of personal bankruptcy filings tend to encourage bankruptcy lawyers to set up practices.
2. (2/3)63 = 8.06 * 10-12, or 1 in 124 billion.
3. The binomial probability is
|2 positive||1 positive, 1 negative||2 negative||Total|
6. E[profit] = ($1000 - $10,000) P + $1,000(1 - P) = $1,000 - $10,000 implies P > 0 if P < 0.10.
7. The z values are
8. Think of each slot as numbered 1, 2, ..., 9:
9. There is clearly selection bias; for example, those whose first language isn't English are less likely to read this newspaper.
10. For a histogram, we should divide the 100 annual data into a small number of categories, such as 0-10 inches, 10-20 inches, and so on. The density is the fraction of the total number of years with rainfall in that interval, divided by the interval width.