Question: Of the people who are 65+ yrs old, are at least 10% employed?
So say the population is 100, if 20 are 65+ yrs old, the question is that are at least 10% of them (i.e. 2 people) employed?

(1) In country X, 11.3 percent of the population is 65 year old or older
Doesn't tell us anything about employment. Not sufficient.

(2) In country X, of the population 65 year old or older, 20 percent of the men and 10 percent of the women are employed
So this statement talks about only the population which is 65+ yrs old. It says that of those people, of all the men, 20% are employed and of all the women, 10% are employed. So if you take the population of all 65+ yrs old people, can we guess what the employment rate is? It depends on what percent of 65+ people are men and what percent are women. But is there a range in which it must lie? Yes, the rate of employment of all 65+ people will lie between 10% and 20%. If the entire 65+ population is men, then the rate of employment will be 20%. If the entire 65+ population is women, then the rate of employment will be 10%. In case there is a mix of men and women, the rate of employment will lie between 10% and 20%. It will be the weighted average of 10% and 20%.

Answer (B)

This question, though much easier, is similar to the famous piglet question from GMAT Prep. Check it out here: http://www.veritasprep.com/blog/2014/09 ... difficult/