The population of City X doubles every 25 years. If this rate continues for the foreseeable future, how many centuries will it take for the population to increase from 20,000 to 1,280,000?

A. 6
B. 4.5
C. 2.5
D. 2
E. 1.5

The OA is E.

20000, after 25 years 40000, after 25 years 80000, after 25 years 160000, after 25 years 320000, after 25 years 640000, after 25 years 1280000.

So from 20000 to 1280000, it takes 25*6 years i.e 150 years = 1.5 centuries.

Hence option E is the correct answer.

Please, can anyone explain another way to solve this PS question? Thanks in advance.