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700 DS tough question .. really challenging !

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lordzilla Just gettin' started!
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Mon Feb 28, 2011 3:22 am
For me this is a very easy question. Just think about it critically and the answer will jump staight at you in less than 2mins .
Statement 1 alone is sufficient.

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pesfunk Really wants to Beat The GMAT!
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Fri Mar 04, 2011 9:11 am
To get this done within 2 minutes...use the matrix method...it really helps!

meng wrote:
Hi everybody, this is actually a 700 level question ! I hope that you can solve it within 2 min ! if you did .. I can say that your score gonna be around 700

Guests at a recent party ate a total of fifteen hamburgers. Each guest who was neither a student nor a vegetarian ate exactly one hamburger. No hamburger was eaten by any guest who was a student, a vegetarian, or both. If half of the guests were vegetarians, how many guests attended the party?

(1) The vegetarians attended the party at a rate of 2 students to every 3 non-students, half the rate for non-vegetarians.

(2) 30% of the guests were vegetarian non-students.

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Fri Mar 04, 2011 11:21 am
meng wrote:
Hi everybody, this is actually a 700 level question ! I hope that you can solve it within 2 min ! if you did .. I can say that your score gonna be around 700

Guests at a recent party ate a total of fifteen hamburgers. Each guest who was neither a student nor a vegetarian ate exactly one hamburger. No hamburger was eaten by any guest who was a student, a vegetarian, or both. If half of the guests were vegetarians, how many guests attended the party?

(1) The vegetarians attended the party at a rate of 2 students to every 3 non-students, half the rate for non-vegetarians.

(2) 30% of the guests were vegetarian non-students.
Whenever we have groups (in this case, vegatarians and non-vegetarians) that are being divided into smaller groups (in this case, students and non-students), we can use a group grid to organize the data.

Here's what the grid looks like (V = vegetarians, NV = non-vegetarians, S = students, NS = non-students):

In the grid above, every row has to add up to the total, as does every column. Looking at the top row, student vegetarians + student non-vegetarians = total students. Looking at the left-most column, student vegetarians + non-student vegetarians = total vegetarians.

Now let's fill in the data step by step.

Let T = total.
Since half the guests are vegetarians, V = (1/2)T, NV = (1/2)T.
Since the 15 hamburgers were eaten by the non-student NVs, 15 goes in the center box:

Statement 1: The vegetarians attended the party at a rate of 2 students to every 3 non-students, half the rate for non-vegetarians.
Thus, for the NVs, students : non-students = 4:3. This means that 3/7 of the NVs were non-students. Here is what the grid now looks like:

Since in the center box we have (3/7)(1/2)T = 15, we can solve for T.
Sufficient.

Statement 2: 30% of the guests were vegetarian non-students.
No way to determine what fraction of the NVs were non-students.
Insufficient.

The correct answer is A.

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needthis Rising GMAT Star
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Thu Mar 17, 2011 2:15 pm
Stuart Kovinsky wrote:
meng wrote:
Hi everybody, this is actually a 700 level question ! I hope that you can solve it within 2 min ! if you did .. I can say that your score gonna be around 700

Guests at a recent party ate a total of fifteen hamburgers. Each guest who was neither a student nor a vegetarian ate exactly one hamburger. No hamburger was eaten by any guest who was a student, a vegetarian, or both. If half of the guests were vegetarians, how many guests attended the party?

(1) The vegetarians attended the party at a rate of 2 students to every 3 non-students, half the rate for non-vegetarians.

(2) 30% of the guests were vegetarian non-students.
Total = G1 + G2 + neither - both

Applying that formula to the question stem, we get:

# Guests = #students + #vegetarians + neither - both

and we know that

#v = 1/2(#g) and neither = 15, so:

G = S + .5G + 15 - both

So, we have 1 equation and 3 unknowns.

(1) gives us two ratios. What can we do with ratios? Turn them into equations! Now, here's the beautiful thing... we don't care what those equations are, as long as they:

- are linear;
- are distinct; and
- don't introduce any new variables.

Going through our checklist, we see that all 3 criteria are upheld. Therefore, we have 3 distinct linear equations for 3 unknowns: we can solve the entire system, sufficient!
Stuart ,I couldn't really figure out the other two equations.

Using the ratios gives us:
non veg and student/ non veg and non student = 4/3 where non veg and non student =15

veg and student/ veg and non student = 2/3, where veg and student is indeed both in your equation above.

The terms "non veg and student" and "veg and non student' are indeed introducing new variables to the equation system.
Or I got totally confused here?

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Thu Mar 17, 2011 2:22 pm
needthis wrote:
Stuart ,I couldn't really figure out the other two equations.

Using the ratios gives us:
non veg and student/ non veg and non student = 4/3 where non veg and non student =15

veg and student/ veg and non student = 2/3, where veg and student is indeed both in your equation above.

The terms "non veg and student" and "veg and non student' are indeed introducing new variables to the equation system.
Or I got totally confused here?
Hi,

it's been a while since I made that post, so forgive me if I'm a bit rusty on this one!

Remember, we an add the following equations as well:

non veg = total - veg
non student = total - student

So, if you consider those two things you mentioned "new" variables, we can solve for them using the information/variables that we already have.

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sayanchakravarty Just gettin' started!
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Fri May 27, 2011 6:10 am
For veg

S:NS = 2:3

For non veg

S:NS = (2:3)*2 , since veg is half the rate for non veg
S:NS = 4:3

Now draw the grid with the info we know ie, NV + NS = 15 (hamburgers)
Therefore, from the non veg category we have

4:3 = x:15
x = 4:3 * 15 = 20

___ | __S__ | __NS__ |
_V_ | __?__ | __?___ |
_NV_ | __20__| __15__ |

Since 15 + 20 is the total no of non vegetarians, we can say vegetarian are also 35 (since half the guests are veg)

Therefore total no of guests = 70

A alone is sufficient

amit.trivedi@ymail.com GMAT Destroyer!
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Sun May 29, 2011 5:59 am
Good question and i got the answer in 5 mins. I know that is quiet bad.

emf_jay Just gettin' started!
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Wed Jul 13, 2011 3:12 am
good Q

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ready for 750 score .... !!!

amit2k9 GMAT Destroyer!
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Wed Jul 13, 2011 9:18 pm
----V-------!V
S--2---------1-

!S-3---------3
----0.5x---0.5x--- x

thus 1:3 = s!v/15 = s!v=5
thus sv=10 thus A is sufficient.

b only gives ratio for SV/!SV. not sufficient.

A it is.

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Deependra1 Rising GMAT Star
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Thu Aug 25, 2011 9:18 am
ANSWER: E

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Thu Aug 25, 2011 9:34 am
Deependra1 wrote:
ANSWER: E
Nope! Its A, why is it E?

prateek_guy2004 GMAT Destroyer!
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Thu Aug 25, 2011 10:33 am
Its a clear ques of overlapping

Group 1 + group 2 +Both - neither

Statement 1 provides 3 equations..We dont really bother how to solve them but it can be solved.

Statemnt 2 insufficient.

Answer A

way2ashish Rising GMAT Star
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Fri Sep 30, 2011 7:19 pm
This was a good one...
Nice excerise and learning

s1s1s1 Just gettin' started!
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Mon Oct 31, 2011 12:11 pm
not that hard in about one minute.
by a glance, stm 2 clearly is NOT sufficient.
stm 1 has everything needed to solve the problem, even without solving the problem.

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Thu Nov 10, 2011 8:51 pm
NS= Non-Student
NV= Non-Veg
S= Student
V=Veg
Student No Hamburger ->
Vegeterian No hamburger -> So all hamburgers are eaten by Non Vegeterians as above no Student ate hamburgers..So all the Non-Veg who ate hamburgers were Non-student=15(NS and NV)
(S and NV)=x

A)
so 2/3=1/2*(S and NV)/(NS and NV)
or 2/3 =1/2*(x/15)
x=20
Therefore Total NV=20+15=1/2 of the Guests
(A) is sufficient

(B) Clearly Insufficient. Total No of guests unknown

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