Shortcut Trick
Net annual growth rate = Birth rate − Death rate = 9% − 7% = 2%.
Effective growth for 2 years using successive formula (x + y + xy/100) = 2 + 2 + (2 × 2)/100 = 4.04%.
Final Population = 2,25,000 × (100 + 4.04)% = 2,25,000 × 1.0404 = 2,34,090.
∴ The correct answer is 234090.
Alternate Method
Given:
Initial population (P) = 2,25,000
Annual Birth Rate = 9%
Annual Death Rate = 7%
Time (n) = 2 years
Formula Used:
Net Rate (R) = Birth Rate − Death Rate
Final Population = P × (1 + R/100)n
⇒ Net Rate of growth (R) = 9% − 7% = 2% per annum
⇒ Population after 1st year = 2,25,000 × (1 + 2/100) = 2,25,000 × 1.02 = 2,29,500
⇒ Population after 2nd year = 2,29,500 × (1 + 2/100) = 2,29,500 × 1.02
⇒ Final Population = 2,34,090
∴ The correct answer is 234090.
Additional Information
Net Growth Rate
When both birth and death rates are given, the net annual growth is calculated by subtracting the death rate from the birth rate.
Population Change Formula
The population after 'n' years is given by Pn = P(1 ± R/100)n, where P is initial population and R is rate of change.
Successive Percentage Change
If a value changes by x% and then y%, the effective percentage change is (x + y + xy/100)%.