Zoo Animals - Easy but a tricky one

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 269
Joined: Thu Sep 19, 2013 12:46 am
Thanked: 94 times
Followed by:7 members

Zoo Animals - Easy but a tricky one

by mevicks » Mon Oct 14, 2013 3:26 am
In a certain zoo, the number of giraffes is 40% the number of chimps, and the number of lions is 55% the number of zebras. If it is given that the number of zebras is approximately 90% the number of chimps, which of the following can be true?

A) For every chimp, there are approximately 2 lions present
B) For every 5 lions, there are approximately 6 giraffes present
C) For every 4 lions, there is exactly one giraffe present
D) For every 5 lions, there are approximately 4 giraffes present
E) For every 4 giraffes, there is a lion present

OA D

Regards,
Vivek
Last edited by mevicks on Mon Oct 14, 2013 4:25 am, edited 1 time in total.
Source: — Problem Solving |

User avatar
Master | Next Rank: 500 Posts
Posts: 490
Joined: Thu Jul 04, 2013 7:30 am
Location: Chennai, India
Thanked: 83 times
Followed by:5 members

by Uva@90 » Mon Oct 14, 2013 3:53 am
mevicks wrote:In a certain zoo, the number of giraffes is 40% the number of chimps, and the number of lions is 55% the number of zebras. If it is given that the number of zebras is approximately 90% the number of chimps, which of the following can be true?

A) For every chimp, there are approximately 2 lions present
B) For every 5 lions, there are approximately 6 giraffes present
C) For every 4 lions, there is exactly one giraffe present
D) For every 5 lions, there are approximately 4 giraffes present
E) For every 4 giraffes, there is a lion present

OA after a few responses

Regards,
Vivek
Hi Vivek is OA D ?

Senior | Next Rank: 100 Posts
Posts: 81
Joined: Tue Jun 11, 2013 10:24 pm
Thanked: 7 times
Followed by:1 members

by sanjoy18 » Mon Oct 14, 2013 4:04 am
Let chimps=200
Giraffes= 80
Zebras= 180
Lions= 99

Now Lion is to Girafffe = 99:80
= 5:4 (approximately)
Hence D

Master | Next Rank: 500 Posts
Posts: 269
Joined: Thu Sep 19, 2013 12:46 am
Thanked: 94 times
Followed by:7 members

by mevicks » Mon Oct 14, 2013 4:25 am
Smart Numbers Approach:
Let C = 100
G = 40
Z = 90
L = 0.55 * 90 = 50 approx
For every 5 lions there are 4 giraffes.

Algebraic Approach:

G = 0.4 C
L = 0.55 Z
Z = 0.9 C (approx)

Do a quick vertical scan of the answers, we need the relationships C--L & L--G. Substitute the above equations to form the relationships
L = 0.55 * 0.9 C = 0.5 C = C/2 (approx)
also from the above relationship C = 2 L
G = 0.4 * 2 L = 0.8 L
Substitute the answer choices to check the relationship, only L = 5 & G = 4 works.

[spoiler]Answer : D[/spoiler]

Regards,
Vivek

User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Mon Oct 14, 2013 4:42 am
mevicks wrote:In a certain zoo, the number of giraffes is 40% the number of chimps, and the number of lions is 55% the number of zebras. If it is given that the number of zebras is approximately 90% the number of chimps, which of the following can be true?

A) For every chimp, there are approximately 2 lions present
B) For every 5 lions, there are approximately 6 giraffes present
C) For every 4 lions, there is exactly one giraffe present
D) For every 5 lions, there are approximately 4 giraffes present
E) For every 4 giraffes, there is a lion present

OA after a few responses

Regards,
Vivek
The number of giraffes is 40% the number of chimps.
G:C = 40:100.
The number of lions is 55% the number of zebras.
L:Z = 55:100.

If Z=C, we get:
G:L:Z:C = 40:55:100:100.
Since Z is actually approximately 90% of C, the values for L:Z must decrease by about 10%:
G:L:Z:C = 40:50:90:100.

G:L = 40:50 = 4:5, supporting answer choice D:
For every 5 lions, there are approximately 4 giraffes present.

The correct answer is D.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

Master | Next Rank: 500 Posts
Posts: 269
Joined: Thu Sep 19, 2013 12:46 am
Thanked: 94 times
Followed by:7 members

by mevicks » Mon Oct 14, 2013 5:03 am
Hi Mitch,

Why is the 10% reduction not made for G:L ?


Regards,
Vivek

User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Mon Oct 14, 2013 12:44 pm
mevicks wrote:Hi Mitch,

Why is the 10% reduction not made for G:L ?


Regards,
Vivek
Only one constraint is given for G:
G:C = 40:100.
When the ratio is altered from G:L:Z:C = 40:55:100:100 to G:L:Z:C = 40:50:90:100, G:C = 40:100 in each case, so there is no reason to change the value of G.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3