Critical Reasoning

The barge captain always stops before entering the lock. If the warning light is not flashing and there are no other boats in the lock, he enters the lock. If the warning light is not flashing but there are other boats in the lock, the barge captain waits until these boats go through and the lock is clear before entering.
If the above statements are true and it is true that the barge stops at the entrance to the lock but does not enter it, which of the following do we know to be a possible reason for not entering?

A) The warning light is flashing and the lock is clear.

B) The warning light is flashing and the lock is not clear.

C) The warning light is not flashing and the lock is not clear.

D) The warning light is flashing, or the lock is not clear, or both.

E) The warning light is not flashing or the lock is not clear.

IMO C

Has to be D!

D

Both conditions must exist in order to enter lock i.e. 1) Warning lights not flashing 2) No boats in the lock. If either 1 or 2 (or both) don't exist, then he won't enter lock.

It's like saying in order to live you must eat and breathe. If you're told that someone died, then it must be that A) they only ate and didn't breathe, or B) they only breathed and didn't eat, or C) they did neither.

Logical Critical Reasoning......

It has to be Either Or condition......

Either the Warning light is ON Or the lock is not clear...
OR
Both the conditions exists.....

Option D states this.

Great explaination @lewsym

IMO C
Assuming that both conditions must exist is assuming too much...From the passage we know that the lock has to be empty for the captain to enter.
It is not stated in the passage that warning light is one of the conditions. It is possible that the captain completly ignores the warning light

C is the only answer we can be sure of...

gkammaje wrote:IMO C
Assuming that both conditions must exist is assuming too much...From the passage we know that the lock has to be empty for the captain to enter.
It is not stated in the passage that warning light is one of the conditions. It is possible that the captain completly ignores the warning light

C is the only answer we can be sure of...

I disagree with your conclusion, but I agree that this is a horribly worded question and therefore there's ambiguity.

"Which of the following do we know to be a possible reason for not entering?"

I suppose that the "do we know" part of the question could be interpreted as "what's a definite reason why". In fact, that's the way it has to be interpreted to arrive at (d). However, a "possible reason" is anything that hasn't been categorically ruled out, so any answer that mentions the light flashing is a "possible reason" why he's not entering the lock (since we have no info about what the captain does when the light IS flashing).

Ambiguity aside, (d) is the answer that's logically supported by the information we're given.

We have the rule:

If the light isn't flashing AND there are no boats, the captain will enter.

Another way to state this rule is:

If the captain does not enter, then either the lights are flashing or there are boats.

(For the formal logic geeks in the crowd, this interpretation is called the "contrapositive", something you generally do NOT need to know for the GMAT but which is essential for the LSAT. If you're studying using LSAT logical reasoning material, either you've come across the term before or you should find new material!)

We know that the captain does not enter, so at least one of the results must be true as well:

The lights are flashing;
there are boats in the dock; or
the lights are flashing and there are boats in the dock.

Choose (D).

thanks for the great explaination -
I am still confused I guess...
(since we have no info about what the captain does when the light IS flashing). How can we be 100% sure that the captain will not enter if the light is flashing?

We are sure that the captain will not enter if the lock is not clear -

Answer choice D says one possible reason is - Just the light is flashing but the lock is not clear... :S

I am curious about the source and OA of this question....

IMO D. OA pls.

I'm not so sure about the source of this question and IMO C. Because the question doesn't say what he does if the warning is flashing! How can we infere hw won't enter because of that? That's not written anywhere....

I would go with option D as the correct option