ExplanationEvery 3 minutes, the population increases by 20% (which is the same as multiplying by 1.2).
Beginning at 8:54am, this change would occur at 8:57am and again at 9:00am. Use the variable x to represent the original quantity. Note that the 20% increase occurs twice:
x(1.2)(1.2) = 144,000
x = 100,000
Note that you cannot just reduce 144,000 by 20% twice, because 20% is not a percent of 144,000—it is a percent of the unknown, original number.
Alternatively, begin from 144,000 and calculate “backwards”:
From 8:57am to 9:00am: y(1.2) = 144,000, so y =\(\frac{144,000}{1.2}\) = 120,000.
From 8:54am to 8:57am: z(1.2) = 120,000, so z = \(\frac{120,000}{1.2}\)= 100,000.
_________________
SandyIf you found this post useful, please let me know by pressing the Kudos ButtonTry our free Online GRE Test