Hi swerve,

We're told that in the first half of the 20th century, the population of a particular country increased by 200 percent and in the second half of the century, the population increased by 300 percent. We're asked for the TOTAL percent increase in population of this country in the 20th century. This question can be solved by TESTing VALUES.

To start, let's set the initial population = 100.
A 200% INCREASE would increase this population by 2(100) = 200, so the new population would be 100+200 = 300 people

A 300% INCREASE of this new number would increase this population by 3(300) = 900, so the end population would be 300+900 = 1200 people

The percentage increase for the entire century would be (1200 - 100)/(100) = 1100/100 = 11 = 1100%

Final Answer: D

GMAT assassins aren't born, they're made,
Rich

swerve wrote:In the first half of the 20th century, the population of a particular country increased by 200 percent. In the second half of the century, the population increased by 300 percent. What was the percent increase for the 20th century as a whole?

(A) 500%
(B) 600%
(C) 800%
(D) 1100%
(E) 1200%

The OA is D.

Please, can any expert explain this PS question for me? I have many difficulties to understand why that is the correct answer. Thanks.

We can let the population be 100 at the beginning of the 20th century. Thus, at the end of the 20th century, the population was (notice that a 200 percent increase means 3-fold and a 300 percent increase means 4-fold):

100 x 3 x 4 = 1200

Thus, the percent increase for the 20th century as a whole is:

(1200 - 100)/100 x 100

1100

Answer: D