(1) Of the boys in the class, 15 are studying biology.
(2) The number of girls in the class is twice the number of students in the class who
are not studying biology.
Can someone explain why the answer is C & not E. Thanks!
Target Test Prep is 20% off right now!
Use code FLASH20
Available with Beat the GMAT members only code
MORE DETAILS
The table above shows the number of students in a certain hi
This topic has expert replies
-
mitzwillrockgmat
- Master | Next Rank: 500 Posts
- Posts: 124
- Joined: Wed May 19, 2010 10:20 pm
- Thanked: 3 times
- GMAT Score:1100
The table below shows the number of students in a certain high school class who are boys and the number of students in the class who are studying biology. What is the total number of students in the class?
(1) Of the boys in the class, 15 are studying biology.
(2) The number of girls in the class is twice the number of students in the class who
are not studying biology.
Can someone explain why the answer is C & not E. Thanks!
(1) Of the boys in the class, 15 are studying biology.
(2) The number of girls in the class is twice the number of students in the class who
are not studying biology.
Can someone explain why the answer is C & not E. Thanks!
-
liferocks
- Legendary Member
- Posts: 576
- Joined: Sat Mar 13, 2010 8:31 pm
- Thanked: 97 times
- Followed by:1 members
From 1
Of the boys in the class, 15 are studying biology
total number of boys =18
so Of the boys in the class, (18-15) or 3 are not studying biology
and Of the girls in the class, (26-15) or 11 are studying biology
but we still dont know how many girls are not studying biology...not sufficient
From 2
clearly not sufficient
combining,
from 1
let Of the girls in the class, x are not studying biology
so total x+3 students not studying biology
and numbers of girls in the class 11+x
from 2 11+x=2(3+x)
or x=5
So total student in class=15+3+11+5=34..sufficient
Ans option C
Of the boys in the class, 15 are studying biology
total number of boys =18
so Of the boys in the class, (18-15) or 3 are not studying biology
and Of the girls in the class, (26-15) or 11 are studying biology
but we still dont know how many girls are not studying biology...not sufficient
From 2
clearly not sufficient
combining,
from 1
let Of the girls in the class, x are not studying biology
so total x+3 students not studying biology
and numbers of girls in the class 11+x
from 2 11+x=2(3+x)
or x=5
So total student in class=15+3+11+5=34..sufficient
Ans option C
"If you don't know where you are going, any road will get you there."
Lewis Carroll
Lewis Carroll
-
mitzwillrockgmat
- Master | Next Rank: 500 Posts
- Posts: 124
- Joined: Wed May 19, 2010 10:20 pm
- Thanked: 3 times
- GMAT Score:1100
you are awesome!!liferocks wrote:From 1
Of the boys in the class, 15 are studying biology
total number of boys =18
so Of the boys in the class, (18-15) or 3 are not studying biology
and Of the girls in the class, (26-15) or 11 are studying biology
but we still dont know how many girls are not studying biology...not sufficient
From 2
clearly not sufficient
combining,
from 1
let Of the girls in the class, x are not studying biology
so total x+3 students not studying biology
and numbers of girls in the class 11+x
from 2 11+x=2(3+x)
or x=5
So total student in class=15+3+11+5=34..sufficient
Ans option C
I encountered the same problem in one of my tests and am not sure if the answer is either C or E.
B alone can solve the problem.
If the number of students who are not studying biology is taken as 'x', then the number of girls in the class is '2x'.
Equating numbers on both sides (since total no of students who take bio + those who don't take bio = no if boys + girls in class)
2x+18 = x + 26
We can solve for 'x' and hence get the total no of students.
B alone can solve the problem.
If the number of students who are not studying biology is taken as 'x', then the number of girls in the class is '2x'.
Equating numbers on both sides (since total no of students who take bio + those who don't take bio = no if boys + girls in class)
2x+18 = x + 26
We can solve for 'x' and hence get the total no of students.
-
DeepthiRajan
- Junior | Next Rank: 30 Posts
- Posts: 27
- Joined: Sat Feb 06, 2010 1:55 pm
- Thanked: 5 times
IMO the answer is (B). As the previous poster has correctly noted, from (2) we get:
If number of students not studying biology =x
then number of girls = 2x
we have: 26+x = 18+2x
x=8
therefore, total number of students = 26+x = 34
If number of students not studying biology =x
then number of girls = 2x
we have: 26+x = 18+2x
x=8
therefore, total number of students = 26+x = 34
-
mitzwillrockgmat
- Master | Next Rank: 500 Posts
- Posts: 124
- Joined: Wed May 19, 2010 10:20 pm
- Thanked: 3 times
- GMAT Score:1100
Hi , I just tried this problem again & it has come to my attention that the answer should in fact be B!DeepthiRajan wrote:IMO the answer is (B). As the previous poster has correctly noted, from (2) we get:
If number of students not studying biology =x
then number of girls = 2x
we have: 26+x = 18+2x
x=8
therefore, total number of students = 26+x = 34
but the answer provided is C.
I don't know the source of this question so if any one knows the source & the provided answer, pls let me know!! thanks
GMAT/MBA Expert
-
Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
mitzwillrockgmat wrote:The table below shows the number of students in a certain high school class who are boys and the number of students in the class who are studying biology. What is the total number of students in the class?
(1) Of the boys in the class, 15 are studying biology.
(2) The number of girls in the class is twice the number of students in the class who
are not studying biology.
ASIDE: Since the diagram closely resembles a Double Matrix Method diagram, I'll treat it as such.
Target question: What is the total number of students in the class?
Statement 1: Of the boys in the class, 15 are studying biology.
Add this information to our diagram to get:
Since the top row must add to 18, we know that the top-right box must have 3 students.
Also, since the left-hand column must add to 26, we know that the bottom-left box must have 11 students.
Add this information to the diagram to get:
At this point, we still don't have a value for the bottom-right box, which means that are many possible scenarios. Here are two possible scenarios:
In the left-side diagram, there is a total of 49 students
In the right-side diagram, there is a total of 129 students
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: The number of girls in the class is twice the number of students in the class who are NOT studying biology.
We can add this information to our diagram as follows:
KEY CONCEPT #1: the sum of the rows must equal the sum of the columns.
So, we can write: 18 + 2x = 26 + x
Solve to get: x = 8
KEY CONCEPT #2: the total number of students = the sum of the two rows
So, the total number of students = 26 + 8 = 34
The answer to the target question is there are 34 students in the class
Since we can answer the target question with certainty, statement 2 is SUFFICIENT
Answer: B
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
