das.ashmita wrote:In 2010, City X urban planners expected the city's population to increase by 20% per year over the three years that followed. If that projection were to come true, the population in 2012 would be exactly triple the population in 2009. Which of the following is the approximate percent population increase in City X from 2009 to 2010?
20%
45%
72%
108%
124%
OA D
Let the 2010 population be 100
2011 population = 120 (added 20% of 100)
2012 population = 144 (added 20% of 120)
We're told that the 2012 population is 3 times the 2009 population.
If the 2012 population is 144, then the 2009 population is about 50.
Important: I
could have been more precise and calculated the 2009 population as 144/3, but I'd rather not work with such a clunky value. Since the
answer choices are sufficiently spread apart, I can be somewhat aggressive with my estimation.
So, the 2009 population is about 50, and the 2010 population is 100.
This represents a 100% increase from 2009 to 2010.
When I check the answer choices, I see that only
D is close to 100%. So, the correct answer must be
D.
Cheers,
Brent
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