Need some help in understanding how to solve this GRE question.
Question: The population of a country increases at a fixed percentage each year.
Column A: Increase in population in the first decade $1980-1990$.
Column B: Increase in population in the second decade $1990-2000$.
It is a quantitative comparison question, i.e, I have to compare Column A with Column B. IF Col A > Col B the answer is A. If Col A < Col B the answer is B, if both equal then the answer is C, and if there is not enough information to compare them, then the answer is D.
My answer at first was (C) i.e. both columns are equal, but Column B is greater than Column A is the correct answer.
So why is the correct answer B? That is, Column B > Column A.
Let's say the population increases by 10% a year, and at the start of 1980, it had exactly 1 million people in it.
In the year 1980, the population increases by 10% of 1 million. By the end, there are 1.1 million people in the country.
In the year 1981, the population increases by 10% of 1.1 million. By the end, there are 1.21 million people in the country.
The population grows more in later years, because it's growing by the same percentage of a larger number.