If the population of an African country is 45 million and its land area is 900,000 km², what is its population density?

Population density is calculated by dividing total population by total land area: $45{,}000{,}000 \div 900{,}000 = 50$ persons per km². Option A (40) and D (55) are common arithmetic errors, while B (45) confuses population figures with the density result.