[求助]天山4-28看了讨论还是不服

stellaleigh

T-4-Q28

In Berinia, the age at which people could begin to drink alcohol legally used to be 18. In 1990, in an attempt to reduce alcohol consumption and thereby to reduce alcohol-related traffic deaths among Berinians under 21, the legal drinking age was raised to 21. Alcohol-related traffic deaths among people under 21 have decreased significantly since 1990. nevertheless, surveys show that people in that age-group drink just as much alcohol as they did before 1990.u

Which of the following, if true of Berinia, most help to resolve the apparent discrepancy?

For the population as a whole, annual alcohol consumption is no lower now than it was in 1990

Alcohol consumption away from home, for example in bars and restaurants, is much lower among people under 21 than it was in 1990

The proportion of people under 21 who own a car is higher now than it was in 1990

Alcohol consumption is lower among people under 21 than among adults in most other age-groups.

Alcohol-related traffic deaths among people over 21 have increased slightly since 1990.

答案是B，我认为是C。看了以前的讨论。不服！

在酒吧饭店里面喝酒仍旧可以驾车啊

而C不就是有车的人多，喝酒的人属不变（分子不变分母增加），然后traffic death related to alcohol 的比率少了吗？

yaoyao99

The problem with C is that:
X = total number of people under 21 in Berinia
Y% = total percent of people who drinks (remains relatively constant)
A% = total percent of car owners under the 21 BEFORE the change in legal drinking age
B% = total percent of car owners under the 21 AFTER the change

The amount of people who can drink and drive before: X * Y * A
The amount of people who can drink and drive after: X * Y * B
Based on the condition that B > A we can conclude that after > before, doesn't explain the decrease in alcohol-related traffic death.

bluegold998

It's said that "Alcohol-related traffic death ... decreased" not rate.Although choice C may explain the rate decreased, it cannot tell us why the number decreased.

stellaleigh

以下是引用yaoyao99在2006-5-5 21:09:00的发言：
The problem with C is that:
X = total number of people under 21 in Berinia
Y% = total percent of people who drinks (remains relatively constant)
A% = total percent of car owners under the 21 BEFORE the change in legal drinking age
B% = total percent of car owners under the 21 AFTER the change

The amount of people who can drink and drive before: X * Y * A
The amount of people who can drink and drive after: X * Y * B
Based on the condition that B > A we can conclude that after > before, doesn't explain the decrease in alcohol-related traffic death.

谢谢完全懂了。

yaoyao99

Excellent, =)

stellaleigh

问一下MM，真的实战中恐怕无法又那么空闲的时间想那么多，MM是怎么思考一些文章有些坳的题目的？

yaoyao99

I always figure out the constant factors first, stop paying attention to them and then focus on what's changed.  Without listing out the formulas, you can figure out that X and Y remained constant.  So focus on the only thing that changed (car owners) and see how it affects the overall result (accidents).

stellaleigh

thanks.I believe it is an effective way.

Good luck for you