At a time when the population of the world was given as 5.3 billion, the largest city, Mexico City, had around 21.5 million inhabitants, New York was fourth largest with some 15.7 million, Rio de Janeiro was tenth largest with 11.9 million.Question 21Which of the following options is the closest estimate of the percentage of the world’s population that lived in the ten largest cities?Under 0.5%Between 0.5% and 2%Between 2% and 4%Over 4%

To answer this question, we need to make an estimate based on the information given. We know the population of the 1st, 4th, and 10th largest cities, but we don't know the population of the 2nd, 3rd, 5th, 6th, 7th, 8th, and 9th largest cities.

However, we can make an educated guess. Let's assume that the population of these cities falls linearly from the 1st to the 10th. This means that the 2nd and 3rd cities have populations somewhere between 21.5 million (Mexico City) and 15.7 million (New York), and the 5th to 9th cities have populations somewhere between 15.7 million and 11.9 million (Rio de Janeiro).

If we take the average of the populations of Mexico City and New York, we get (21.5 + 15.7) / 2 = 18.6 million. Let's assume this is the average population of the 2nd and 3rd largest cities. So, the total population of the 1st to 3rd largest cities is approximately 21.5 + 18.6 + 18.6 = 58.7 million.

Similarly, if we take the average of the populations of New York and Rio de Janeiro, we get (15.7 + 11.9) / 2 = 13.8 million. Let's assume this is the average population of the 5th to 9th largest cities. So, the total population of the 4th to 10th largest cities is approximately 15.7 + 5*13.8 = 84.7 million.

Adding these together, we get an estimated total population of the ten largest cities of 58.7 + 84.7 = 143.4 million.

The world population is given as 5.3 billion, which is 5300 million. So, the percentage of the world's population that lived in the ten largest cities is (143.4 / 5300) * 100 = 2.7%.

Therefore, the closest estimate is "Between 2% and 4%".