74. The number of North American children who are obese, that is who have more body fat than do 85 percent of North American children their age, is steadily increasing according to four major studies conducted over the past 15 years.
If the finding reported above is correct, it can be properly concluded that
(A) when four major studies all produce similar results those studies must be accurate.
(B) North American children have been progressively less physically active over the past 15 years.
(C) The number of North American children who are not obese increased over the past 15 years.
(D) Over the past 15 years, the number of North American children who are underweight has declined.
(E) The incidence of obesity.
Another inference question, so the same rules apply - we're looking for a statement that MUST be true based on one or more of the facts in the stimulus.
We start by paraphrasing the stimulus:
Four major studies tell us that the NUMBER (my emphasis) of N.A. children who are obese is steadily increasing. Obesity is defined as children heavier than 85 PERCENT (my emphasis) of their peers.
On most inference questions, it's very difficult to predict the correct answer (since, on the basis of a bunch of facts, there's usually numerous conclusions that can be drawn). Here, however, if we notice the distinction between numbers and percents, we may be able to make a rough prediction.
If obesity is a relative concept (i.e. it's not a fixed weight, it's your weight relative to the weight of others), how can the group comprising that top 15% get bigger? Only if the entire pool of children grows.
So, our prediction: there must be more children now than there were previously.
Going through the choices, (C) should jump out as the clear winner - not an exact match for our prediction, but following the same logic.
A quick look at the other choices:
A) "must be accurate" - too extreme, eliminate.
B) we have no info on the causes of obesity - outside the scope, eliminate.
D) we have no info on how the other 85% of children are distributed (maybe all 85% are underweight) - outside the scope, eliminate.
E) answer choice incomplete.
Remember, the correct answer to an inference question MUST be true; if you read a choice and think "well, this COULD be true, but I'm not sure", then you can confidently eliminate that choice.