Population Growth
The population of any country does not remain constant.
It generally increases. The relative increase of population over an interval of
time is called population growth. Growth per unit time is called growth rate.
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The way of increasing population is exactly similar to
the way of increasing compound amount, because, every year population increases
from the previously increased population also.
So, the population of a country or place after T years
is given by the formula,
Where, P ----------> Initial population
PT
---------> Population after T years
R
----------> Rate of growth in % per year
T
----------> Time in no. of years
The growth of population is also affected by the number of
deaths, in-migrants and out-migrants at the end of the given period of time. In
this case,
Where,
D ------------> Number of deaths
Min
----------> In-migrants
Mout ---------> Out-migrants
Some other formula,
Workout Examples
Example 1: The population of a town
before 2 years was 75000 and the rate of annual growth of population of the
town is 2%. If the number of in-migrants and out-migrants at the end of 2 years
were880 and 625 respectively and 550 people died within this time interval,
find the present population of the town.
Solution: Here,
P = 75000
R = 2%
Min = 880
Mout = 625
D = 550
PT = ?
We have,
= 75000 × 1.0404 – 550 + 880 – 625
= 78030 – 550 + 880 – 625
= 77735
So,
the present population of the town is 77735
Example 2: The present population of a
town is 40000. If the yearly birth rate is 5% and death rate is 3%, what will
be the population of town after 2 years?
Solution: Here,
P = 40000
R1 = 5%, R1
= 3%
T = 2 years
PT = ?
We have,
= 40000 × 1.0404
= 41616
So,
the population of the town after 2 years will be 41616.
Example 3: The population of a village
increases every year by 5%. At the end of two years, the total population of
the village was 10000. If 1025 were migrated to other places, what was the
population of the village in the beginning?
Solution: Here,
Total population
including the migrated number,
PT = 10000 + 1025 = 11025
R = 5%
T = 2 years
Present population, P =
?
We have,
or, 11025 = P (1.05)2
or, 11025 = P × 1.1025
or, P = 11025/1.1025
or, P = 10000
So,
the population of the village in the beginning was 10000.
Example 4: The population of a town
before 3 years was 150000. If the annual growth rates of the population in the
last 3 years were 2%, 4% and 5% respectively every year, find the population of
the town at the end of 3 years.
Solution: Here,
P = 150000
R1 = 2%, R2 = 4% and R3
= 5%
T = 3 years
PT = ?
We have,
= 150000 × 1.02 × 1.04 × 1.05
= 167076
So,
the population of the town at the end of 3 years is 167076.
Example 5: 3years ago, the population of
a village was 50000. The population growth rate of village is 2% p.a. 1 year
before 420 people died due to an epidemic. Find the present population of the
village.
Solution: Here,
P = 50000
R = 2%
After 2 years (i.e. 1 year before), T = 2 years
After 2 years, 420 people died due to epidemic. So,
P = 52020 – 420 = 51600
Then, after 1 year (i.e.
at present), T = 1 years
So,
the present population of the village is 52632.
You can comment your
questions or problems regarding the population growth here.
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