This one is tricky, but I believe the answer is E. Let me attempt to explain.

Let's look at (1) first. There are two possibilities here: A is a truth-teller, or he is a liar. If he is a truth-teller, this creates a contradiction: he states that only one other person is a liar, when we know there are clearly two liars, and a truth-teller would state as such. So this cannot be correct.

If he is a liar, we have to look at both ways this statement could be a lie. The first possibility is that there are other liars BESIDES C, but this cannot be the case, because we know there are only two liars, and we have accounted for both: A and C. The other lie is that C is a truthteller.

SO, from statement (1), we have learned that A is a liar and C is a truthteller, but nothing about B and D. So (1) is insufficient.

Let's look at statement (2). Two possibilities: B is a truthteller, B is a liar. If B is a truthteller, everything works out fine, but we don't yet know if he is. Darn. If him lying creates a NECESSARY contradiction, then (2) is sufficient, but a quick glance shows that it does not; B would obviously HAVE to be lying, because there is more than one truth-teller. So (2) is not sufficient. The only two answers left are C) and E).

Since C) Requires BOTH (1) and (2) to be used in conjunction, let us apply what we have learned from (1) to the second statement. If B is the truth-teller, what he says is true, and there is no contradiction. If B is the liar, he is lying in that both C and D are truth-tellers. Since both of these scenarios work out, there is no way to know even from both statements, and thus the answer is E.

Not totally positive here, but that's my best shot. It's a hell of a logic puzzle for a two-minute limit, too.

Yes your answer is correct.
Its E

a quick glance shows that it does not; B would obviously HAVE to be lying, because there is more than one truth-teller.

how you can say so firmly that B is lying?

If he is telling truth then statement 2 is sufficient.

Not an expert(that would have to be a Stuart/Ian/Ron/Stacey/Jim) but I will certainly try to help. For logic probs like these consider all possibilities with the limited info available

Given: A B C D (2 speak the truth & 2 lie)

Stmt I

If A is the truth teller then all we know is C is one liar. We have no info on B and D

INSUFF(since we cant come up with 1 definite list)

Stmt II

If B is the truth teller then all we know is C is other truth teller.
A D -> LIARS

If B is a liar then we know C must be a truth teller. We have no info on where A and D fall

INSUFF(since we cant come up with 1 definite list)

Together:

No idea if A is truth teller or B which changes C's position i.e can be a liar or truth teller

Atleast a couple of combinations possible among A B C D

INSUFF

Choose E
INSUFF

I don't know that he's lying. Because there was no contradiction with him telling the truth, the only way (2) would be sufficient is if there is NO WAY he could possibly be a liar, i.e., him being a liar would create a contradiction. We can rule this out pretty quick. If he is a liar, what he is saying would HAVE to be a lie, because there are obviously two truth-tellers out there. So this does not create a contradiction. Hence it is possible that B could be both a truth-teller or a liar (unlike in (1), where A could ONLY be a liar), we don't know which, and thus (2) is insufficient.

I think the trick here is that each fact can lead us to both cases, or the statement is a liar, or not. So we can choose B alone, Is that right ?

I think the trick here is that each fact can lead us to both cases, or the statement is a liar, or not. So we can choose B alone, Is that right ?

The answer is E.
Thanks Cramya.
For proper explanation to this question, please refer to the post made by Cramya.

As for all of you I have yet another tricky question

Among A,B,C and D, is B the second tallest person if no two persons are of the same height?
1.) The height of one person is the average of heights of A and B.
2.) The height of A is the average of the heights of two persons.

Answer with Proper Explainations

gmat740 wrote:Among A,B,C and D, is B the second tallest person if no two persons are of the same height?
1.) The height of one person is the average of heights of A and B.
2.) The height of A is the average of the heights of two persons.

Answer with Proper Explainations

1) tells us that someone is between A and B. Therefore, either A or B (or both) is 1st or 4th. However, we could have B 2nd and A 4th ("yes") or B 1st and A 4th ("no"): insufficient.

2) nothing about B: insufficient.

Together:

From (2), we know that A is either 2nd or 3rd (since A must be between two other people). From (1) we know that either A or B must be 1st or 4th. Combined, B must be either 1st or 4th, so B is definitely NOT 2nd: sufficient, choose (C).