I don't know why they bothered to calculate the actual populations, but you don't really need to. Just add the percentages up, or given that it looks to scale, on the actual UMAT you could even use a ruler and add the distances of each bar together to figure out which make the greatest population potentially even faster. The only part where you might need a calculator is in the male/female ratio, but just consider them separately and you'll see that the answer is greater in both the male and female populations individually anyway so it doesn't matter. The only part where it would get confusing and quite unfair is if the male population of one answer was greater than another, but not the female.