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.
If the candidate visit O last, which of the following could be the first and third cities on her schedule , respectively ?

Options

A. J and L
B. J and O
C. L and N
D. L and O

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."
Start by entering the additional information on a diagram:
`{:("1 2 3 4 5 6"),(" K O "):}`
Next, we have already determined that M cannot be earlier than fifth:
`{:("1 2 3 4 5 6"),(" K M O "):}`
Next, since J must precede N, there are three possibilities:

(1) describes the second of these possibilities. The other choices do not describe one of the three possible schedules.