The number of North American children who are obese—that is, who have more body fat than do 85 percent of North Ameri...

Steven on March 24 at 06:14PM

I’m pretty lost on this one

How can we infer that the number of kids who aren’t obese has increased in the past 15 years? I think to myself—with an increasing proportion of obese kids, the proportion of non-obese kids would decrease. I just want to know how you thought about it. Thanks!

1 Reply

on March 24 at 10:09PM

Hello @Henleys,

This is a very important lesson. It is an example of LSAT math, and I can almost guarantee that you will come across something like it on your test. Most of LSAT math comes down to one thing: an understanding of percentages/rates vs. total number. This is certainly something worth practicing.

Let's consider the definition of childhood obesity: having more body fat than 85% of North American children. So, no matter what, the obese children are going to make up 15% of the population. Let's say that ten years ago there was a child population of 100. 15 would be obese, 85 would not be obese.

We are then told that the number of obese children has increased. Let's say that there are now 30 obese children. How can 30 children make up 15% of the population? Only if the total population is 200. There are now 170 non-obese children. This is why C is correct. I think that you misused the word proportion. Because of the definition of obesity, the proportion has remained exactly the same! The number of obese kids increased, but the proportion of obese kids has not.

This is kind of a trick question, because the stimulus appears to make a claim about children becoming more obese. However, it is really only saying that the total population has grown.