[求助]天山4-28看了讨论还是不服

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.

yaoyao99

Excellent, =)

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).