What is the richest country per capita?

One-third of the people from country a claim that they are from country b, and the rest admit they are from country a. one-fourth of the people from country claim that they are from country a, and the rest admit they are from country b. in a combined census of the two countries, one-half of the total claimed to be from a. what is the ratio of the populations of country a to that of country b.

When turned about its axis of rotation, which shape could have created this three-dimensional object?

Why is causation so much more difficult to prove than correlation?