Population with opposite successive changes: Town population = 126800. It increases by 15% in the first year and decreases by 20% in the second year. What is the population after 2 years?
Aptitude
Percentage
Difficulty: Easy
Choose an option
-
A174984
-
B135996
-
C116656
-
D145820
-
E126800
Answer
Correct Answer: 116656
Explanation
Introduction / Context:Successive percent changes multiply, not add. We apply the 15% increase then the 20% decrease to the base 126800.
Given Data / Assumptions:
- Initial population = 126800.
- Year 1 factor = 1.15.
- Year 2 factor = 0.80.
Concept / Approach:Final population = 126800 * 1.15 * 0.80 = 126800 * 0.92.
Step-by-Step Solution:
Compute 126800 * 0.92.126800 * 92/100 = (1268 * 92) = 116656.Therefore, population after 2 years = 116656.Verification / Alternative check:Increase by 15%: 126800 → 145820; then decrease by 20%: 145820 * 0.8 = 116656. Both methods agree.
Why Other Options Are Wrong:
- Other values do not match the exact factor 0.92 applied to 126800.
Common Pitfalls:Adding −20% and +15% to get −5% and multiplying once; this ignores compounding on different bases.
Final Answer:116656