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LSAT分析推理之官网样题（四）

2016-05-10 11:48

来源：LSAC

作者：

新东方网LSAT频道在此与大家分享LSAC官网上公布的LSAT分析推理样题（四），希望对大家备考LSAT分析推理有所帮助。

**Passage for Questions 5 and 6**

From a group of seven people—J, K, L, M, N, P, and Q—exactly four will be selected to attend a diplomat’s retirement dinner. Selection conforms to the following conditions:

Either J or K must be selected, but J and K cannot both be selected.

Either N or P must be selected, but N and P cannot both be selected.

N cannot be selected unless L is selected.

Q cannot be selected unless K is selected.

**Question 5**

If P is not selected to attend the retirement dinner, then exactly how many different groups of four are there each of which would be an acceptable selection?

one

two

three

four

five

**Explanation for Question 5**

This question adds a new supposition to the original set of conditions—“P is not selected to attend the retirement dinner.” The task is to determine all of the different possible selections that are compatible with this new supposition. A compatible solution is one that violates neither the new supposition nor the original conditions.

Since the second condition states “[e]ither N or P must be selected ...,” we can infer from the new supposition (P is not selected) and the second condition (either N or P, but not both, is selected) that N is selected. And since N is selected, we know from the third condition that L is selected. In other words every acceptable selection must include both L and N.

We are now in a good position to enumerate the groups of four which would be acceptable selections. The first condition specifies that either J or K, but not both, must be selected. So you need to consider the case where J (but not K) is selected and the case in which K (but not J) is selected. Let’s first consider the case where J (but not K) is selected. In this case, Q is not selected, since the fourth condition tells you that if K is not selected, then Q cannot be selected either. Since exactly four people must be selected, and since P, K, and Q are not selected, M, the only remaining person, must be selected. Since M’s selection does not violate any of the conditions or the new supposition, N, L, J, and M is an acceptable selection; in fact, it is the only acceptable selection when K is not selected. So far we have one acceptable selection, but we must now examine what holds in the case where K is selected.

Suppose that K is selected. In this case J is not selected, but Q may or may not be selected. If Q is selected, it is part of an acceptable selection—N, L, K, and Q. If Q is not selected, remembering that J and P are also not selected, M must be selected. This gives us our final acceptable selection—N, L, K, and M.

Thus there are exactly three different groups of four which make up acceptable selections, and (C) is the correct response.

This was a difficult question, based on the number of test takers who answered it correctly when it appeared on the LSAT.

**Question 6**

There is only one acceptable group of four that can be selected to attend the retirement dinner if which one of the following pairs of people is selected?

J and L

K and M

L and N

L and Q

M and Q

**Explanation for Question 6**

The way in which this question is phrased is rather complex, and so it is important to get very clear what exactly is being asked. Unlike other questions which give you a new supposition to consider in conjunction with the original conditions, this question asks you to determine what is needed, in addition to the original conditions, to guarantee that only one group of four is acceptable.

One way to approach this question is to consider each option individually, and determine for each option whether only one acceptable group of four can be selected when the pair indicated in the option is selected. You may wish to vary the order in which the options are considered according to personal preferences. In the discussion here, we will consider the answer choices in order from (A) through to (E).

Choice (A): When both J and L are selected, K cannot be selected (first condition). Consequently Q cannot be selected (fourth condition). More than one group of four is acceptable under these circumstances, however: J, L, M, and N may be selected, and J, L, M, and P may be selected.

Choice (B): When K and M are both selected, J cannot be selected (first condition). Other than that, anyone else could be selected. This leaves more than one acceptable group of four. K, L, M, and N may be selected; K, L, M, and P may be selected; and K, M, P, and Q may be selected.

Choice (C): When L and N are both selected, P cannot be selected (second condition), but, as in the case of option (B), anyone else can be selected. This leaves more than one acceptable group of four: J, L, M, and N may be selected; K, L, M, and N may be selected; and K, L, N, and Q may be selected.

Choice (D): When L and Q are both selected, K must be selected (fourth condition). Consequently J cannot be selected (first condition). Either N or P must be selected (second condition), and there is nothing that rules out either N or P from being selected here. So, more than one group of four is acceptable under these circumstances: K, L, N, and Q may be selected, and K, L, P, and Q may be selected.

Choice (E): When M and Q are both selected, K must be selected (fourth condition), and hence J cannot be selected (first condition). Furthermore, N cannot be selected: if N were selected, then L would also have to be selected (third condition), and this would violate the restriction that exactly four people are to be selected. And since N cannot be selected, P must be selected (second condition). Thus when M and Q are both selected, both K and P must be selected as well, and only one group of four—K, M, P, and Q—is acceptable. (E) is therefore the correct response.

This was a very difficult question, based on the number of test takers who answered it correctly when it appeared on the LSAT.

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