So the grove is split two ways into Northern half-Southern half and Western half-Eastern half. Think of a circle split horizontally into 2 parts and also vertically into two parts.
Using both statements, we know that there are 18 trees in the northern half so there must be 18 in the southern half. We also know that there are 18 trees in the eastern half and so there must be 18 in the western half.
For ease, let's assume each quadrant has 9 trees.


The average yield in the northern half is 60 and average yield in the eastern half is 55. Note that 9 trees (in red) overlap in northern and eastern halves. We have no idea about the yield of the south west quadrant. Hence this is certainly not sufficient. Also, we don't know how many trees actually overlap and the yield of those trees.

Answer (E)
_________________

I also go with E. the south west corner is missing

can someone explain why? and if the southwest corner was given how would we have calculated the yield.

I think the OA is incorrect and that it should be C.

This is a weighted average question, and we can calculate the yield per tree for the 36 trees when (1) and (2) are combined. The simple reason is that the two regions are distinct and together account for all 36 pecan trees.

(1/2)*60+(1/2)*55 = 57.5

Posted from my mobile device

The correct answer is E. Check here: http://gmatclub.com/forum/if-a-certain- ... l#p1279526
_________________

Just because north and east is mentioned we will assume there is West and South as well? And who says the shape of the grove is a circle or rectangle or anything?
The grove can be a circle but trees can only be in north and east with no overlap.
I am okay with answer being E but I don't like the question.
_________________

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________