The number of North American children who are obese - that is, who hav

OFFICIAL EXPLANATION

This stimulus provides information about both the numbers and percentages of obese children, and so you can end up with an answer that has either a number or a percentage (though a numerical answer is more likely since the percentage is fixed at a constant 15% in the stimulus). The numerical information comes from the phrase, “The number of North American children who are obese...is steadily increasing.” The percentage information comes from the phrase, “children who are obese—that is, who have more body fat than do 85 percent of North American children their age.” The percentage information defines obese children as those who fall into the top 15% among all children their age in terms of body fat, and therefore the percentage is known to be constant. The numerical information tells us that the actual number of obese children is increasing (and since this is a Must Be True question we can accept that information as accurate).

Answer choice (A): This answer is incorrect because there is no evidence in the stimulus to support it. Although the stimulus mentioned four major studies that apparently agreed about the increase in the number of obese children, it would be an exaggeration to say that any time four major studies produce similar results they must be accurate.

Answer choice (B): This answer proposes a causal reason for why the number of obese children is growing. From the information in the stimulus we cannot determine the cause of the rise in obesity, so answer choice (B) is also wrong.

Answer choice (C): This is the correct answer. Consider the following example: 15 years ago—100 total children of similar age

Number of obese children 15 = 15%
Number of non-obese children 85 = 85%

Now, let us say that the number of obese children has risen to 150 children today: So far we have conformed to the information given in the stimulus: the actual number of obese children is rising. However, although the number of obese children has now risen to 150, the definition of obesity (“more body fat than 85 percent of North American children”) remains unchanged. Since this is the case, the 150 obese children today must still comprise the top 15% of the total child population. Consequently, the remaining 85% of non-obese children must now be 850 (150 is 15% of 1000, and thus 85% of 1000 is 850):

Answer choice (C) is fully supported because the stimulus provides information about both the number and percentage of obese children. As stated earlier, if the stimulus provides information about both the numbers and percentages in a situation, then you can select any supported answer choice that contains either numbers or percentages. Note the emphasis on the word “supported.” In the obesity problem, GMAC could easily have written an incorrect answer choice that says, “The number of North American children who are not obese decreased over the past 15 years.”

Answer choice (D): This answer addresses “underweight” children, who are neither defined nor discussed in the stimulus.

Answer choice (E): This answer is directly contradicted by the information in the stimulus, which states that the incidence of obesity is definitionally set at a constant 15%.