Answer:
To calculate the population doubling time, we can use the rule of 70. The rule of 70 states that the doubling time can be estimated by dividing 70 by the growth rate.
In this case, the growth rate is 2.5%. To convert it to a decimal, we divide it by 100: 2.5/100 = 0.025.
Now, we can calculate the doubling time using the rule of 70:
Doubling time = 70 / growth rate
Doubling time = 70 / 0.025
Doubling time ≈ 2800 years
Therefore, in this country with a population of 8 billion and a growth rate of 2.5%, the population doubling time is approximately 2800 years.