Final answer:
The time it took for the world population to double once again cannot be determined based on the information provided. However, there has been an acceleration in population growth over the years.
Step-by-step explanation:
The information provided is not sufficient to determine how long it took for the world population to double once again after going from 0.25 billion people to 0.50 billion people in 1649 years. However, based on the information provided, we can see that the time it takes for the population to double has been decreasing over the years.
According to the information, it took 123 years to add 1 billion people in 1930, and then it only took 24 years to add 2 billion people between 1975 and 1999. This indicates an acceleration in population growth. However, it is important to note that population growth is predicted to slow in the coming decades.
Therefore, we cannot determine the exact time it took for the population to double once again based on the information provided. However, we can infer that it would likely be less than 1649 years due to the acceleration in population growth.