The largest city in Brazil, Sao Paulo, has a population of about 11 million. Based on the rank-size rule, what is the population of the second-largest city, Rio de Janeiro, most likely to be?

The rank-size rule estimates a city’s population by dividing the largest city’s population by its rank. For the second-largest city, divide 11 million by 2 to get about 5.5 million. Therefore, Rio de Janeiro is most likely to have a population of 5–6 million.

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