Is most of the land in City A zoned residential?

Expert replies

jaymw: Master | Next Rank: 500 Posts; Posts: 144; Joined: Sun Aug 29, 2010 9:17 amFollowed by: 4 members; Thanked: 40 times; GMAT Score:760

by jaymw » Tue Dec 21, 2010 10:25 pm

Source: Kaplan

Is most of the land in City A zoned residential?

(1) All land in City A is zoned as either residential or commercial
(2) The proportion of land zoned residential in City A could be tripled

OA after some discussion

Like this post

Source: Beat The GMAT — Data Sufficiency | Tue Dec 21, 2010 10:25 pm

Night reader: Legendary Member; Posts: 1337; Joined: Sat Dec 27, 2008 6:29 pmFollowed by: 10 members; Thanked: 127 times

by Night reader » Tue Dec 21, 2010 10:39 pm

jaymw wrote:Source: Kaplan

Is most of the land in City A zoned residential?

(1) All land in City A is zoned as either residential or commercial
(2) The proportion of land zoned residential in City A could be tripled

OA after some discussion

I am after choice E

question: call residential R and Commercial C, then is R>C?
st(1) precisely gives that R+C=Total Lands i.e. only R and C in the set are present; we need the relationship between R and C. Not Sufficient.
st(2) precisely gives that R could become 3*R then C must be C-2*R; again missing the relationship between R and C, as it's possible 3*R < or > or = (C-2*R), moreover we don't what are the other parameters in the set (e.g. some D or F...) Not sufficient.

Combining st(1&2) Not sufficient.

Last edited by Night reader on Tue Dec 21, 2010 11:35 pm, edited 1 time in total.

Like this post

GMAT/MBA Expert

Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members; Location: Milpitas, CA; Thanked: 447 times

by Rahul@gurome » Tue Dec 21, 2010 11:19 pm

Solution:
Let the part which is residential be x and let the other part be y.
We need to know whether x > y or not.
Consider first (1) alone.
We just get that y is commercial.
Obviously, it is not sufficient alone because we do not know how much part is residential and how much part is commercial.
Next consider (2) alone.
We only come to know that x can become 3x which will be less than total land area but we do not come to know whether x > y or not.
Next combine both the statements together and check.
On combining we get that total land area is x + y where x is residential and y is commercial.
Now since x can become 3x, we will have that 3x <= x + y.
Or 2x <= y.
Since x and y are positive, we conclude that x < y.
So most of the area is not residential.

The correct answer is (C).

Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)

Like this post

Night reader: Legendary Member; Posts: 1337; Joined: Sat Dec 27, 2008 6:29 pmFollowed by: 10 members; Thanked: 127 times

by Night reader » Tue Dec 21, 2010 11:43 pm

I have just made minor edition to my solution which does not change approach. Below I would like to test my solution as Rahul came with C and I find E as the only possible choice.

question: call residential R and Commercial C, then is R>C?
st(1) precisely gives that R+C=Total Lands i.e. only R and C in the set are present; we need the relationship between R and C. Not Sufficient.
st(2) precisely gives that R could become 3*R then C must be C-2*R; again missing the relationship between R and C, as it's possible 3*R < or > or = (C-2*R), moreover we don't what are the other parameters in the set (e.g. some D or F...) Not sufficient.

Combining st(1&2) Not sufficient.

testing for choice C with 2 alternatives:
1) suppose initially R=2 and C=9, then after changed proportion 3*R or 3*2 and C-2*R or 9- (3*2) => new R=6 and new C=5 => R>C because 6>5
2) suppose initially R=2 and C=11, then after changed proportion 3*R or 3*2 and C-2*R or 11- (3*2) => new R=6 and new C=7 => R<C because 6<7

Therefore, we need relationship between R and C to decide if R < or = or > C

Like this post

GMAT/MBA Expert

Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members; Location: Milpitas, CA; Thanked: 447 times

by Rahul@gurome » Tue Dec 21, 2010 11:55 pm

Night reader wrote:I have just made minor edition my solution which does not change approach. Below I would like to test my solution as Rahul came with C and I find E as the only possible choice.

question: call residential R and Commercial C, then is R>C?
st(1) precisely gives that R+C=Total Lands i.e. only R and C in the set are present; we need the relationship between R and C. Not Sufficient.
st(2) precisely gives that R could become 3*R then C must be C-2*R; again missing the relationship between R and C, as it's possible 3*R < or > or = (C-2*R), moreover we don't what are the other parameters in the set (e.g. some D or F...) Not sufficient.

Combining st(1&2) Not sufficient.

testing for choice C with 2 alternatives:
1) suppose initially R=2 and C=9, then after changed proportion 3*R or 3*2 and C-2*R or 9- (3*2) => new R=6 and new C=5 => R>C because 6>5
2) suppose initially R=2 and C=11, then after changed proportion 3*R or 3*2 and C-2*R or 11- (3*2) => new R=6 and new C=7 => R<C because 6<7

Therefore, we need relationship between R and C to decide if R < or = or > C

But we need to know whether original value of R is more than original value of C or not.
In 1) R=2 < C=9 and 2) R = 2 < C = 11.

In both case it is not.

Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)

Like this post

Night reader: Legendary Member; Posts: 1337; Joined: Sat Dec 27, 2008 6:29 pmFollowed by: 10 members; Thanked: 127 times

by Night reader » Wed Dec 22, 2010 12:12 am

Thanks Rahul, I would be misled if not for your expertise

this holds true for R<C always, choice C

Like this post

jaymw: Master | Next Rank: 500 Posts; Posts: 144; Joined: Sun Aug 29, 2010 9:17 amFollowed by: 4 members; Thanked: 40 times; GMAT Score:760

by jaymw » Wed Dec 22, 2010 1:07 am

OA is indeed C.

Great explanation, Rahul!

Like this post

Woozler: Senior | Next Rank: 100 Posts; Posts: 43; Joined: Sat Nov 06, 2010 12:04 pm

by Woozler » Wed Dec 22, 2010 11:22 am

Even after Rahul's explanation I still don't get it why it's not (B). If land zoned residential could be tripled then it means that only one third or less of all land in city A is currently zoned residential.

Like this post

GMAT/MBA Expert

Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members; Location: Milpitas, CA; Thanked: 447 times

by Rahul@gurome » Wed Dec 22, 2010 6:56 pm

Woozler wrote:Even after Rahul's explanation I still don't get it why it's not (B). If land zoned residential could be tripled then it means that only one third or less of all land in city A is currently zoned residential.

.

Just consider statement (2) alone.
It means that there can be a third type of area apart from residential and commercial.
Suppose initially residential area R is 8, commercial area C is 2 and some other part say X is 36.
Next if R can be tripled, we can have that R is 24, C is 2, and X is 20.
Here originally R > C.
Now suppose R is 5, C is 6, and X is 36.
If R can be tripled, we can have that R is 15, C is 6, and X is 26.
Here originally R < C.
So from (2) alone nothing definite can be said whether R > C or not.

Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review