Of all the students in a certain dormitory, are first-year : PS Archive
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 24 Jan 2017, 06:56

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Of all the students in a certain dormitory, are first-year

Author Message
Manager
Joined: 20 Mar 2005
Posts: 170
Followers: 2

Kudos [?]: 71 [0], given: 0

Of all the students in a certain dormitory, are first-year [#permalink]

### Show Tags

29 Sep 2007, 04:58
00:00

Difficulty:

(N/A)

Question Stats:

80% (01:57) correct 20% (00:00) wrong based on 36 sessions

### HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Of all the students in a certain dormitory, ½ are first-year students and the rest are second-year students. If 4/5 of the first-year students have not declared a major and if the fraction of second-year students who have declared a major is 3 times the fraction of first-year students who have declared a major, what fraction of all the students in the dormitory are second-year students who have not declared a major?
A. 1/15
B. 1/5
C. 4/15
D. 1/3
E. 2/5
Senior Manager
Joined: 27 Aug 2007
Posts: 253
Followers: 1

Kudos [?]: 12 [0], given: 0

### Show Tags

29 Sep 2007, 06:40
1
This post was
BOOKMARKED
It is B,

1/2 * 1/5 = 1/10 - first year who declared major
3/10 - second year who dec. major
1/2 - 3/10 = 2/10=1/5 portion of total students who is 2-year and did not declared major

Ans: B
VP
Joined: 08 Jun 2005
Posts: 1146
Followers: 7

Kudos [?]: 189 [0], given: 0

### Show Tags

29 Sep 2007, 07:19
Plug in:

Total students ---> 100

first year ---> 50 ---> declared a major 10 ---> not declared a major 40

second year ---> 50 ---> declared a major 30 ---> not declared a major 20

second-year students who have not declared a major ---> 20/100 = 1/5

Last edited by KillerSquirrel on 29 Sep 2007, 07:29, edited 1 time in total.
SVP
Joined: 28 Dec 2005
Posts: 1575
Followers: 3

Kudos [?]: 148 [0], given: 2

### Show Tags

29 Sep 2007, 07:23
im curious as to where i went wrong:

i started with the info of 4/5th not having selected a major, which gives me:

4/5*(1/2)=2/5 of 1st yrs havent decided a major

This means that 3/5 of 1st yrs have

If the fraction of 2nd yrs who have is 3 times what the first yrs have, this gives me

3*3/5 = 9/5 !!!
VP
Joined: 08 Jun 2005
Posts: 1146
Followers: 7

Kudos [?]: 189 [0], given: 0

### Show Tags

29 Sep 2007, 07:36
pmenon wrote:
im curious as to where i went wrong:

i started with the info of 4/5th not having selected a major, which gives me:

4/5*(1/2)=2/5 of 1st yrs havent decided a major

This means that 3/5 of 1st yrs have

If the fraction of 2nd yrs who have is 3 times what the first yrs have, this gives me

3*3/5 = 9/5 !!!

this is a non sequitur ! since 1-2/5 = 3/5 will give you P(second year declared a major)+P(second year not declared a major)+P(first year declared a major) and not ---> P(first year declared a major) = 3/5

Director
Joined: 09 Aug 2006
Posts: 763
Followers: 1

Kudos [?]: 193 [0], given: 0

### Show Tags

01 Oct 2007, 11:26
Balvinder wrote:
Of all the students in a certain dormitory, ½ are first-year students and the rest are second-year students. If 4/5 of the first-year students have not declared a major and if the fraction of second-year students who have declared a major is 3 times the fraction of first-year students who have declared a major, what fraction of all the students in the dormitory are second-year students who have not declared a major?
A. 1/15
B. 1/5
C. 4/15
D. 1/3
E. 2/5

B.

used a double set matrix.
Column 1 = 1 st yr
Column 2 = 2 nd yr
Row 1 = Decl. Major
Row 2 = Not Decl.

Column 3 and Row 3 = Total.

If total = x; 1st yr = 1/2x; 2nd yr = 1/2x
1st yr not decl = 2/5 x
1 st yr decl = 1/2x - 2/5x = 1/10x
2nd yr decl = 3/10 x
2nd yr not decl = 1/2x - 3/10x = 1/5x
Re: PS - fraction   [#permalink] 01 Oct 2007, 11:26
Display posts from previous: Sort by