A candidate for public office plans to visit each of the six cities J, K, L, M, N and O exactly once during her campaign. Her aides are setting up the candidate's schedule according to the following restrictions :
The candidate can visit M only after she has visited both L and N.
The candidate cannot visit N before J.
The second city visited by the candidate must be K.
Which of the following could be true of the candidate's schedule ?

Options

A. She visit J first.
B. She visit Kfirst.
C. She visit L sixth.
D. She visit M fourth.

Answer

A

Explanation

Begin by summarising the infrormation: `(L+N)ltM`
`JltN`
K=2
Note: Since the candidate cannot visit two simultaneously, the condition " The candidate cannot visit N before J" is equivalent to " She must visit J before N."
This question is a good occasion to talk about test-taking strategy. A question of this form has this peculiarity : a choice like (1) may not contradict any single initial condition and may still be wrong because of the way the initial conditions work together. The only way to exclude this possibility is to device a complete order, part of which is the segment you want to test-a - time - consuming process. What should you do ?
The solution to the dilemma is this : Make a first run through the choices, testing them by each single initial statement. If you can eliminate all but one, then you have your correct answer. If more than one choice remains, then the key to the question is some interaction among the initial conditions, e.g., a further inference that you have overlooked. Then, and only then, try working up an entire order to test the remining choices. Here, we are fortunate because we can find the correct choice quickly:
1) 1) Doesn.t contradict any single condition. So go to the next choice.
2) No.(K must be second.)
3) No.(L must come before M.)
4) No. (M must come after J. L and N, and therefore K as well . So M cannot be visited earlier than fifth.)
5) No: (N must come before M, so N cannot be last.)
Thus, (1) must be the correct choice, so we don.t have to try to construct the entire order using (1).
Just for reasons of completeness of explanation, however, here is a schedule in which J is the first city:
`{:("1 2 3 4 5 6"),("J K L N M O "):}`