Math Quiz: NYT Learning Network

Through Math for America, I am part of an on-going collaboration with the New York Times Learning Network.  My latest contribution, a Test Yourself quiz-question, can be found here:

https://learning.blogs.nytimes.com/2012/04/30/test-yourself-math-april-30-2012/

This question is based on rapid population growth in African countries.  How long will it take Nigeria’s population to quadruple?