Q12 - The number of North American

[opulence2001]

Hi,

I have read over this question a couple of times and I cannot see why D is wrong and C is right. C seems like the opposite.
If we know that the number of obese children has increased over the last 15 years, how can we conclude that the number of children non-obese has increased? We don't know if these non-obese children are just fat, or average or underweight. Non-obese children is a large category so I can't see how we can conclude that numbers have increased here. Maybe all increases are in the obese category only.

I originally chose D, but I see that this cannot be drawn now either for the reasons stated above.

[noah]

Thanks for the question.

This is a tricky question, and I actually think that it's easier to eliminate answers then wrap your head around the right one. But let's try both:

This is in an inference question, so no argument, just facts. The facts are that the number of obese kids is growing. That makes sense. We also find out the definition of obese -- quick, what do you think the definition of obese is? You probably think it's something about percent body fat, BMI index, or a certain weight -- interestingly, the given definition of obese is about how kids weight relates to the rest of the population's weight. Let's imagine that during the test, you think that's too complex to dig into immediately, let's eliminate answers then:

(A) this seems too broad - why can we conclude that just because these four studies agree? Maybe in another situation that wouldn't be true. Out of scope as it's focusing on the validity of the studies.

(B) is extrapolating. Just because the kids are obese doesn't mean they're not active - maybe they just eat a lot.

(C) something about the number of non-obese. We'll leave this since that's part of the comparison.

(D) brings in a new topic - underweight! Who's to say that if you're not obese you're underweight? That's actually a pretty twisted idea if you think about it!

(E) is out of scope - this is not about age.

So, just by looking for wrong answers we are down to (C).

The reason that (C) can be inferred is this:

Imagine that there are 100 kids, and 15 kids have more body fat than 85 of the others. Those 15 are obese.

Now, let's imagine that the number of obese kids jumps to 30. Can we just say that those 30 kids have more body fat than the remaining 70 kids? What's the problem with that? Think about that before reading on.

If we have a 30-70 split, than some of those 30 kids are not qualifying as obese. For example, the least fat kid among that 30 will have more body fat than 60 percent (since 60/100 is 60%). So, to have the number of obese kids jump from 15 to 30, we would need the number of non-obese kids to jump too. Let me challenge you to figure out what the number would have to be...

Anyway, does that make sense?

[aaronwfrank]

Now, let's imagine that the number of obese kids jumps to 30. Can we just say that those 30 kids have more body fat than the remaining 70 kids? What's the problem with that? Think about that before reading on.

If we have a 30-70 split, than some of those 30 kids are not qualifying as obese. For example, the least fat kid among that 30 will have more body fat than 60 percent (since 60/100 is 60%). So, to have the number of obese kids jump from 15 to 30, we would need the number of non-obese kids to jump too. Let me challenge you to figure out what the number would have to be...

Anyway, does that make sense?

Nope.

[ohthatpatrick]

They defined obese as essentially: "top 15% fattest kid for kids your age"

Because of that definition, you could never have 20% of kids be obese.

The definition forces it to ALWAYS be 15% are obese and 85% are not. If there were 100 eight year olds, they could go up and down in weight, and we'd always just be saying "the top 15 fattest are the obese ones".

The average weight of the kids could go from 80 lbs. to 120 lbs., and we would STILL only say that 15 of them are obese, because it's a comparative distinction. It's not an absolute number, it's just "you're fatter than 85% of the kids your age".

Again, if we have 100 eight year olds, there will ALWAYS be 15 obese ones, and 85 non-obese ones. Those numbers will never change, no matter how the weights of the 100 kids fluctuate. What might change is WHICH kids are among the 15 obese ones, but the total number will never change, because it will always be 15% of the total kids.

So if the stimulus tells us that now there are MORE than 15 obese kids, we know that the total kids had to go up.

If, for example, there were 200 eight year olds, 30 would be obese and the remaining 170 would be non-obese.

We can't JUST increase the number of obese kids while keeping non-obese kids constant, or else the percentages would be off.

If we had 30 obese and (the original) 85 non-obese, then
30/115 = approx 24% are obese
85/115 = approx 76% are non-obese

The definition doesn't allow that. It's always a 15% / 85% split.

[YudeS218]

So what's the meaning of FOUR MAJOR STUDIES mentioned in the stimulus?
I know it's just a LSAT question and we should not take it too serious, but it's really stupid. Under that definition, there is nothing about obese, just the percentage.
I think it's not a good question.

[LaurenL251]

Hi!

Does this make sense?

• obese: more body fat than the majority (85%) of the total kids
• obese is 15% of the population
• average or anything under obese is 85% of the population

2004: 100 kids total: 85 kids are average and 15 have more body fat (obese) than those 85 average kids.
2019: 200 kids total: 170 kids are average and 30 have more body fat (obese) than those 170 average kids.

The stimulus said the number of kids who are obese is increasing...so if that number is increasing it results in both the total number of kids and the number of average kids increasing as well. In order for that increasing number of obese kids still to be 15% of the whole (total kids)?

So if the amount of obese children rises from 15 to 30, they still need to be 15% of a whole, which also makes the average amount of kids rise to meet the 85% of the whole.

It took me way too long to write all oft his math out when I am reviewing the test. How would someone be able to do this quickly during the actual testing time?!? It just didn't click...
I had a problem deciding not to change the percentages. I was thinking during the test that if more kids were becoming obese then it would go form 15% of the population to maybe 20% of the population. At the time I didn't consider the total population growing...

[Misti Duvall]

Question Type:
Inference

Stimulus Breakdown:
According to four major studies over the past fifteen years, the number of North American children who meet the standard for obesity, defined as having more body fat than 85% of children their age, is steadily increasing.

Answer Anticipation:
There's not a lot of information here. It's possible that the answer will have something to do with proportionality, since we don't have the actual numbers (which have probably changed over time since the amount of one group has increased).

Correct answer:
C

Answer choice analysis:
(A) Too extreme. We can't sure for sure that the studies are accurate.

(B) Out of scope. There's no information about physical activity (nor any speculation about the cause of the increase in obesity).

(C) Correct. If the proportionality has stayed the same (15% obese / 85% not obese) and one group increased, the other must have as well.

(D) Out of scope. There's no information about children who are underweight.

(E) Out of scope. There's no information about change as children grow older.

Takeaway/Pattern:
If you have a group defined by its proportional relationship to another group, look out for an answer about the other group. For example, let's say I have 10 spiders. My star spiders are the ones that can jump higher than 70% of the other spiders. So I have 3 star jumpers and 7 non-star jumpers. If next year I have 6 star jumpers, I must now have 20 total spiders, which means 14 non-stars jumpers.

#officialexplanation