This is great example to highlight the difference between numbers and percents. The stimulus tells us that over the past 15 years the "number of North American children who are obese...is steadily increasing." It also defines obese as "more body fat than do 85 percent of North American children their age."
A simple numerical example will help here. So imagine we had 100 North American children. According to the information, 15 of these students would be considered obese (i.e. the children who have more body fat that 85 percent of North American children) and 85 would be not obese.
Now let's increase the number of obese school children to 30, just as the stimulus tells us. This means that 30 school children have more body fat that 85 percent of North American children. This means that the total number of North American children would be 200 (i.e. 30/200 = .15). If 30 are obese, then 170 are not obese.
As such, it must be true that the number of North American children who are not obese also increased over the past 15 years.
Hope this helps! Please let us know if you have any other questions.
alymathieuOctober 10, 2018
This makes no sense
AnitaOctober 10, 2018
@alymathieu Let’s look at it this way:
They define obesity not by BMI or other measurements, but by weight relative to others. That is, they say obese kids have 85% more body fat than others their age.
They also say the NUMBER of kids with this percentage has grown.
However, all kids together still count for 100%. If there are more people in the 85th percentile than before, that means that there are more people overall, and more people in the non-obese category.
That way, we still end up with 100%.
Does that help?
andreaskormusisJuly 29, 2020
But cant it imply that more of the same kids have gotten fat? Say there are 100 kids in a group, this year 10 are fat. The next year 15 are fat. We didn't add more kids, more kids just got fat.
VictoriaAugust 4, 2020
Hi @andreaskormusis,
It cannot imply that more of the same children have become obese because obesity is defined relative to the entire population of children.
An obese child is defined as one who has more body fat than 85% of North American children their age.
If we had 100 children, this would mean that there would be 15 obese children. If another child gained weight, we wouldn't have 16 obese children; rather, if this child weighed more than another of the 15 obese children, then one of the 15 children would no longer be classified as obese.
Because obesity is defined in this way, an increase in the number of children who are obese can only occur if the total number of children also increases. If the number of children remains the same, then there can only ever be a maximum of e.g. 15 obese children.
Hope this helps clear things up a bit! Please let us know if you have any further questions.
