请教一道题：Prep 2012 - Q57

Jagabee · 发表于 2016-11-19 15:44:22

想请教大家Prep 2012 第57题：

When a city experiences a sharp decline in population, thecity's tax revenues, which pay for such city services as police protection andmaintenance of water lines, also decrease. The area to be policed and thenumber and length of the water lines to be maintained, however, do notdecrease. Attempting to make up the tax revenue lost by raising tax rates isnot feasible, since higher tax rates would cause even more residents to leave.(Prep 12 – 57)

The information given moststrongly supports which of the following general claims?

A. If, in a city with sharplydeclining population, police protection and water line maintenance do notdeteriorate, some other service previously provided by the city willdeteriorate or be eliminated.

B. If a city's tax rates are heldstable over a period of time, neither the population nor the levels of cityservices provided will tend to decline over that period.

C. If a city's populationdeclines sharply, police protection and water line maintenance are the servicesthat deteriorate most immediately and most markedly.

D. A city that suffers revenuelosses because of a sharp decline in population can make up some of the losttax revenue by raising tax rates, provided the city's tax rates are low inrelation to those of other cities.

E. A citythat is losing residents because tax rates are perceived as too high by thoseresidents can reverse this population trend by bringing its tax rates down to amore moderate level.

正选为A. 我的问题:

1. 看了一些资源的解释, 似乎这道题infer的中心变成了推出”虽然某些维护费用不变, 这个city仍能generate tax revenue“的原因. 这是因为原文中说"the city's tax revenue...also decrease" 从而得知即便利润下降，但是利润依然是存在？

2. 原文中说了raising tax rates will cause more residents to leave. 我记得好像逻辑中A 上升时B下降, 是可以反推A下降时B会上升?

请各位指教.

Bradz · 发表于 2016-11-21 09:56:38

第一个问题没看懂。

第二个问题，这个要看题目的说法。比如，A=B-C，那么C上升会导致A下降，同时C下降会导致A上升。这是没错的。但是说C下降一定会导致导致A上升就是错的。E里面的用CAN（without qualifying）可能有点绝对了。另外，个人认为，can reverse真的太难说了，can alleviate可能还比较好接受一点。

Jagabee · 发表于 2016-11-29 10:50:59

Bradz 发表于 2016-11-21 09:56
第一个问题没看懂。

第二个问题，这个要看题目的说法。比如，A=B-C，那么C上升会导致A下降，同时C下降会导 ...

谢谢回复Bradz. 你可以说下你的思路吗？我还是看不出原题是怎么可以infer出A

Tax revenue = tax rate * taxable amount * # of residents – tax expenses
原文只说警力和修水管的这一部分expense不会下降，是怎么可以得出A中信息的？

我的第二个问题是来源于对逻辑中“逆否命题”的困惑，可能也是在哪里模糊听过导致的. 原命题为真, 那么逆否命题也一定成立. 如果原命题为“A上升B会下降，” 那么逆否命题是不是“A下降B会上升？”

Bradz · 发表于 2016-11-29 11:19:06

Jagabee 发表于 2016-11-29 10:50
谢谢回复Bradz. 你可以说下你的思路吗？我还是看不出原题是怎么可以infer出A

Tax revenue = tax rate * t ...

警力和修水管都属于city service，一般来说它们的支出都是来自于税收。首先从题干里我们知道了税收下降。那么能用来支付city service的总额就下降了，如果警力和修水管的支出不变，那么一定有其他city service的支出会下降。

Tax Revenue = Payment in Public Service = Payment in Police + Payment in Pipe Maintenance + Payment in Service A + Payment in Service B + ...... TR下降，Payment in 警力和水管不变，那只能是等式右边的其他某（些）项下降了。写到这，我知道你错在哪里了。你的TR的公式错了，TR等于你等式的第一项，不用减去expenses。

逆否命题不清楚是啥，但是逻辑上来讲，A导致B，不能得出NOT A导致NOT B。我复习了就能及格；但是不复习不一定不及格。

Jagabee · 发表于 2016-11-29 16:13:33

Bradz 发表于 2016-11-29 11:19
警力和修水管都属于city service，一般来说它们的支出都是来自于税收。首先从题干里我们知道了税收下降。 ...

谢谢，我知道我弄混在哪里了. Tax revenue是政府的income而不是”revenue."

但是原文只说“the city's tax revenue, WHICH PAY FOR such city services...," 而不是”the city's tax revenue, which will all be used to pay for ..." 可能我又想到tax revenue可能有盈余, 也可能有别的用途, 感觉很难得出tax revenue=payment in public service的assumption...

而且A中some other service 如果deteriorate, 支出难道不是上升?

Bradz · 发表于 2016-11-30 08:18:19

Jagabee 发表于 2016-11-29 16:13
谢谢，我知道我弄混在哪里了. Tax revenue是政府的income而不是”revenue."

但是原文只说“the city's t ...

A中deterioration是结果。比如政府以前一共有100块来支付10个公共服务，每个公共服务支付10块。现在政府税收下降，只剩下90块，并且警力和水管两方面的支付不下降，那么能付给其他8个公共服务的总支出只剩下70，那么肯定会有至少1个服务收到小于10块，那么这个服务的质量就会变差。

Profit = Revenue - Cost。另外，一般来讲，tax revenue肯定不等于payment in public service，但是这道题里面不涉及其他概念，这么assume也没错。并且，从real world的角度，政府的总收入下降，总支出肯定也随之下降，那么能够支付给公共服务的钱也会按比例下降。

Jagabee · 发表于 2016-12-3 16:00:05

Bradz 发表于 2016-11-30 08:18
A中deterioration是结果。比如政府以前一共有100块来支付10个公共服务，每个公共服务支付10块。现在政府 ...

Bradz，非常感谢，这道题差不多想通了。

请教一道题：Prep 2012 - Q57

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