Lake A has a duck population of 30 females and 36 males. Lake B's duck population consists of the same ratio of females to males. If 6 new female ducks are added to Lake B and no other ducks are added or removed, the new total duck population of Lake B could be which of the following?
A)144
B)105
C)78
D)51
E)36
OAB
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
Lake A and B
This topic has expert replies
-
j_shreyans
- Legendary Member
- Posts: 510
- Joined: Thu Aug 07, 2014 2:24 am
- Thanked: 3 times
- Followed by:5 members
-
GMATGuruNY
- 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
Female ducks : male ducks = 30:36 = 5:6.j_shreyans wrote:Lake A has a duck population of 30 females and 36 males. Lake B's duck population consists of the same ratio of females to males. If 6 new female ducks are added to Lake B and no other ducks are added or removed, the new total duck population of Lake B could be which of the following?
A)144
B)105
C)78
D)51
E)36
Since there are 5 females ducks for every 6 male ducks, the total number of ducks must be a MULTIPLE OF 11.
We can PLUG IN THE ANSWERS, which represent the number of ducks AFTER 6 female ducks are added.
Since before the addition of 6 female ducks the total number of ducks is a multiple of 11, subtracting 6 from the correct answer choice must yield a multiple of 11.
A: 144-6 = 138.
Since 138 is not a multiple of 11, eliminate A.
B: 105-6 = 99.
Success!
The correct answer is B.
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
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
-
j_shreyans
- Legendary Member
- Posts: 510
- Joined: Thu Aug 07, 2014 2:24 am
- Thanked: 3 times
- Followed by:5 members
Hi Guru ,
Thanks for your explanation.
One thing is that why do we take multiple of 11 , we are asked to find the total number of duck from Lake B and multiple of 11 comes from Lake A. Pls advise.
Also can we solve this question through algebra.
Thanks for your explanation.
One thing is that why do we take multiple of 11 , we are asked to find the total number of duck from Lake B and multiple of 11 comes from Lake A. Pls advise.
Also can we solve this question through algebra.
-
GMATGuruNY
- 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
According to the prompt:j_shreyans wrote:Lake A has a duck population of 30 females and 36 males. Lake B's duck population consists of the same ratio of females to males. If 6 new female ducks are added to Lake B and no other ducks are added or removed, the new total duck population of Lake B could be which of the following?
A)144
B)105
C)78
D)51
E)36
Hi Guru ,
Thanks for your explanation.
One thing is that why do we take multiple of 11 , we are asked to find the total number of duck from Lake B and multiple of 11 comes from Lake A. Pls advise.
Lake B's duck population consists of the same ratio of females to males [as Lake A's population].
The words in brackets are omitted, but their presence is implied.
Thus:
(lake B's females : {lake B's males) = (lake A's females) : (lake A's males) = 30:36 = 5:6.
Implication:
In both Lake B and in Lake A, there are 5 females for every 6 males, implying that the total population IN EACH LAKE is a MULTIPLE OF 11.
As noted above, the total population in Lake B must be a multiple of 11.Also can we solve this question through algebra.
Let the original total population = 11x, where x is an integer greater than 0.
After 6 female ducks are added, we get:
New total population = 11x + 6.
Options for the new total population:
17, 28, 39, 50, 61, 72, 83, 94, 105...
Since it's possible that the new total population = 105, the correct answer is B.
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
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
-
Matt@VeritasPrep
- GMAT Instructor
- Posts: 2630
- Joined: Wed Sep 12, 2012 3:32 pm
- Location: East Bay all the way
- Thanked: 625 times
- Followed by:119 members
- GMAT Score:780
We could also do a little algebra here. We know that at Lake B the ratio of females to males is 5 : 6, which we can write as 5x : 6x. After we add 6 female ducks, our ratio is (5x + 6) : 6x. That means the total number of ducks is (5x + 6) + 6x, or 11x + 6. Any answer of this form (in which x is an integer) will work.
144 = 11x + 6 gives x as a fraction
105 = 11x + 6 gives x = 9
78 = 11x + 6 gives x as a fraction
51 = 11x + 6 gives x as a fraction
36 = 11x + 6 gives x as a fraction
So the answer must be B.
144 = 11x + 6 gives x as a fraction
105 = 11x + 6 gives x = 9
78 = 11x + 6 gives x as a fraction
51 = 11x + 6 gives x as a fraction
36 = 11x + 6 gives x as a fraction
So the answer must be B.
GMAT/MBA Expert
-
Jeff@TargetTestPrep
- GMAT Instructor
- Posts: 1462
- Joined: Thu Apr 09, 2015 9:34 am
- Location: New York, NY
- Thanked: 39 times
- Followed by:22 members
We are given that Lake A has a duck population of 30 females and 36 males. Since Lake B's duck population consists of the same ratio of females to males:j_shreyans wrote:Lake A has a duck population of 30 females and 36 males. Lake B's duck population consists of the same ratio of females to males. If 6 new female ducks are added to Lake B and no other ducks are added or removed, the new total duck population of Lake B could be which of the following?
A)144
B)105
C)78
D)51
E)36
f/m = 30/36 = 5/6
Thus, we can let 5x = the number of female ducks in Lake B and 6x = the number male ducks in Lake B. Therefore, the total number of ducks is 11x. We are also given that 6 new female ducks are added to Lake B. We need to check which answer choice could be the total number of ducks after 6 new female ducks are added to Lake B. Keep in mind that x must be an integer.
A. 144
11x + 6 = 144
11x = 138
x = 138/11 = 12 6/11
Since x is not an integer, 144 can't be the total number of ducks in Lake B.
B. 105
11x + 6 = 105
11x = 99
x = 99/11 = 9
Since x is an integer, 105 could be the total number of ducks in Lake B.
Answer: B
Jeffrey Miller
Head of GMAT Instruction
[email protected]
See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
