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:

http://learning.blogs.nytimes.com/2011/02/14/test-yourself-math-feb-14-2011/

This problem is based on comparing the total national incomes of the United States and China.  My solution offers a simple way to turn per capita income and population into meaningful percentages.