[讨论]lsat 4-3-12

12.   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（C）

(E) the incidence of obesity in North American children tends to increase as the children grow older

提干是肥胖儿童的数量增加呢，怎么能推出C，不肥胖儿童的数量也增加了？？？

this is one type of frequently asked question throughtout LSAT and GMAT. the point is to test your understanding about the diffeence between absolute number and percent or proportion.

in this question, the number is increased but its percentage on the overall group is unchanged, 85%.  then, the overall number including bothfat and thin children must increase in a corresponding way.

that is, who have more body fat than do 85 percent of North American children their age

hedonism555 GG 是这句话表明胖小孩所占的比例不变吗？

sorry , i made a mistake. 85% refers to thin children.

But it is the same thing. the thin children's percentage 85% is unchanged but fat one who accounts for 15% increased its absolute number. then, only way to explain this situation is absolute number of thin one also surge.

这道题的关键还是对85%的理解上。

说老实话，我的第一反应是整个体重-人数曲线分配基本没有变，但是thin的更thin了，导致整个均值下降，因此85%分割线前移，使得fat的number增加了。可惜没有适合选项，呵呵

这是个数学题。

看到obses的定义“that is, who have more body fat than do 85 percent of North American children their age”，就应该马上树立起胖人比例永远不变15%的概念，就象GMAT700分一样。

因此，当看到胖人人数增加时，就已经猜到出题人一定是考总人数/胖人/瘦子同比增加的意图了。