Question : From 1980 to 1990, the population of the country increased by 20%. From 1990 to 2000, the population of the country increased by 20%. Over 2000-2010, the population of the country increased by 20%. Then, the overall increased population (in percentage) of the country from 1980 to 2010 was:
Option 1: 72.2%
Option 2: 60%
Option 3: 72.8%
Option 4: 62.8%
Correct Answer: 72.8%
Solution :
For the first two increases of 20% and 20%,
The equivalent increase = (20 + 20 + $\frac{20×20}{100}$)%
= (40 + 4)% = 44% increase
So, from 1980 to 2000, the population increase was 44%
From 1980 to 2010, the increase was 44% and 20%
The equivalent increase = (44 + 20 + $\frac{44×20}{100}$)% = (64 + 8.8)% = 72.8%
Therefore, the population of the country increased by 72.8% from 1980 to 2010.
Hence, the correct answer is 72.8%.
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