Population growth with dual annual increases: A city's population rises at 5% per annum due to natural growth, and there is an additional 5% increase each year due to influx of job seekers (total compounded annually). What is the overall percentage increase in population after 3 years?
Aptitude
Percentage
Difficulty: Easy
Choose an option
-
A33.1%
-
B33%
-
C34%
-
D33.24%
-
E32%
Answer
Correct Answer: 33.1%
Explanation
Introduction / Context:This question tests compound percentage growth when two independent 5% increases act each year. Since both act annually, they combine to a single yearly multiplier and compound over multiple years.
Given Data / Assumptions:
- Natural growth rate per year = 5%.
- Additional influx per year = 5%.
- Effective yearly increase = 5% + 5% = 10% (applied once per year).
- Time = 3 years; compound effect applies.
Concept / Approach:Use compound growth: New population factor after n years = (1 + r)^n. Here r = 10% = 0.10 and n = 3.
Step-by-Step Solution:
Yearly factor = 1 + 0.10 = 1.10.3-year factor = 1.10^3 = 1.331.Overall percentage increase = (1.331 − 1) * 100% = 33.1%.Verification / Alternative check:Apply year by year: after Year 1: 1.10; Year 2: 1.21; Year 3: 1.331. This confirms 33.1% total increase.
Why Other Options Are Wrong:
- 33% and 33.24% are rounding guesses; exact compounding gives 33.1%.
- 34% overstates the growth.
- 32% ignores compounding.
Common Pitfalls:Adding three times 10% (giving 30%) or mixing annual and total increases without compounding.
Final Answer:33.1%