By percentage how much bigger was the population of the north than that of the south

42% (During the civil war period)

Explanation:

The north had a much higher population, as it was more densely populated with big cities, while the south was plantations and farmland.

The North had a population of about 20 million and the South about 9 million.

Actually, slaves made up around 43% of the Southern population.

The slave population among "border states" was not significant.

Delaware as example had less than 1,000.

Answer: about 42%