yumi2012 wrote:James, Sam, Kim and Clark are brothers. Who is the oldest?
A) James is the average age of Sam and Kim
B) Kim is the average age of Sam and Clark

Hi!

What's the source of this question? I'm asking because, technically, the 4 brothers could be quadruplets and all the same age. I really doubt that the question intends for that to be a possibility and the GMAT would never leave that ambiguity in place. Let's assume that the question actually tells us that they're all different ages.

With that out of the way, let's break it down.

Q: Who's the oldest of the 4 brothers?

What do we know? Nothing! So, we need info about all 4 of them.

(1) only provides info about 3 of them: insufficient.
(2) only provides info about 3 of them: insufficient.

So, we very quickly eliminate A, B and D. Hey, even if we're stuck we have a 50/50 shot to get it right.

Since neither statement was sufficient alone, we have to combine. On to combination!

(1) tells us that J is right in the middle of S and K. So, plotting them on a number line we have 2 possibilities:

S --- J --- K
and
K --- J --- S

(2) tells us that K is right in the middle of S and C. Just as above, we get:

S ------ K ------ C
and
C ------ K ------ S

Combining those two together, we see that there are still 2 possibilities:

S ---J---K ------ C
and
C ------ K ---J---S

So, either S or C is the oldest. 2 possible answers is 1 too many, so the correct answer is (E), not enough information.

Stuart

ps: please post data sufficiency questions in the DS forum, not the PS one!