逻辑 Weaken --- 条件型结论--- 不理解，请分析。

girlwithwings

条件型结论：结论带条件（即为充分必要）。

WEAKEN的方法显示充分条件成立，必要条件可以不成立。或举反例，或提供有关信息

对于这个解释不太理解，不知道哪个是充分，哪个为必要。请帮我看看以下是条件型结论吗？
如果是，请帮我分析一下。如果不是，能否举例条件型结论并分析一下呢？
不胜感激。

1

In the United States, of the people who moved from one state to another when they retired, the percentage who retired to Florida has decreased by three percentage points over the past ten years.Since many local businesses in Florida cater to retirees, this decline is likely to have a noticeably negative economic effect on these businesses.

Numbe 与 % 的题

Which of the following, if true, most seriously weakens the argument?

A.Florida attracts more people who move from one state to another when they retire than does any other state.

B.The number of people who move out of Florida to accept employment in other states has increased over the past ten years.

C.There are far more local businesses in Florida that cater to tourists than there are local businesses that cater to retirees.

D.The total number of people who retired and moved to another state for their retirement has increased significantly over the past ten years.

E.The number of people who left Florida when they retired to live in another state was greater last year than it was ten years ago.


Since many local businesses in Florida cater to retirees,--- 充分条件 ？  什么是必要 条件？

2 Lightbox, Inc., owns almost all of the movie theaters in Washington County and has announced plans to double the number of movie screens
it has in the county within five years.Yet attendance at Lightbox’s theaters is only just large enough for profitability now and the county’s population i
s not expected to increase over the next ten years.
Clearly, therefore, if there is indeed no increase in population, Lightbox’s new screens are unlikely to prove profitable.

Clearly, therefore, if there is indeed no increase in population, Lightbox’s new screens are unlikely to prove profitable.

Which of the following, if true about Washington County, most seriously weakens the argument?

A.Though little change in the size of the population is expected, a pronounced shift toward a younger, more affluent, and more entertainment-oriented population is expected to occur.

B.The sales of snacks and drinks in its movie theaters account for more of Lightbox’s profits than ticket sales do.

C.In selecting the mix of movies shown at its theaters, Lightbox’s policy is to avoid those that appeal to only a small segment of the moviegoing population.

D.Spending on video purchases, as well as spending on video rentals, is currently no longer increasing.

E.There are no population centers in the county that are not already served by at least one of the movie theaters that Lightbox owns and operates.

这个呢？ little change in the size of the population --- 是充分条件吗？

haylin

D的理由是  总退休及移居到别州的人口增幅惊人  即使移居到Florida的百分比下降  但是实际上移居的人可能是变多了(number*%)   这是一个数学题
100*20%<120*17%