J, L, M, N, O and P are members of a spy network for security reasons, only certain spies are able to contact other spies. The only contacts allowed are:
J can contact both L and N.
O can be contacted by L, M and P.
N can contact M.
O can contact both L and N.
P can be contacted by M.
A spy can receive a message from any spy who can contact him and , in relay the message to any spy he is able to contact.
Which of the following spies can not be contacted by any other spy in the network ?

Options

A. J
B. M
C. N
D. O

Answer

A

Explanation

Begin with the first condition.
J can contact both L and N:

Next, O can be contacted by L, M and P :

Next, N can contact M :

Then, O can contact both L and N :

Finally, P can be contacted by M:

With a "network" set, any further conclusions that you might need to draw are already implicit in the diagram. For Example, J can have N relay a message to M, who in turn can relay the message to O :

So there is no need to look for further conclusions. Go to the questions.
The diagram shows no arrow leading to J . Which means that J cannot be contacted by anyone (though he can contact others ) . Every other spy can be contacted by at least one other spy.