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probability DS...

by singhpreet1 » Sat Jun 12, 2010 12:30 am
In a group of 30 students, 8 are enrolled in an English class and 16 are enrolled in an Algebra class. How many students are enrolled in both an English and an Algebra class?

(1) 20 are enrolled in exactly one of these two classes.

(2) 3 are not enrolled in either of these classes.

i can result to B. only St. 2 is sufficient, 30-3=27,8+16+24; 27-24, therefore 3 must be studying both..your take guyz...

Preet
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by ankurmit » Sat Jun 12, 2010 1:13 am
ans must be B
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by singhpreet1 » Sat Jun 12, 2010 4:44 am
ankurmit wrote:ans must be B
Ankur: request you to show your working to establish B, though i do agree with your answer!

Thanks.
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by Stuart@KaplanGMAT » Sat Jun 12, 2010 7:46 pm
singhpreet1 wrote:In a group of 30 students, 8 are enrolled in an English class and 16 are enrolled in an Algebra class. How many students are enrolled in both an English and an Algebra class?

(1) 20 are enrolled in exactly one of these two classes.

(2) 3 are not enrolled in either of these classes.

i can result to B. only St. 2 is sufficient, 30-3=27,8+16+24; 27-24, therefore 3 must be studying both..your take guyz...

Preet
The question is flawed. What's the source?

On the GMAT, language is very specific. When we see the phrase "8 are enrolled in an English class", we know nothing else about those people. For example, some of them could also be enrolled in the Algebra class.

Accordingly, statement (2) is impossible. If there are 30 students total, and 8 are in English and 16 in Algebra, then there must be at least 6 people (30 - 24) who aren't enrolled in either class.

If the question stem read "8 are enrolled only in an English class and 16 are enrolled only in an Algebra class", then (2) would make sense (and be sufficient).
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by mj78ind » Fri Jun 18, 2010 6:32 pm
Stuart Kovinsky wrote:
singhpreet1 wrote:In a group of 30 students, 8 are enrolled in an English class and 16 are enrolled in an Algebra class. How many students are enrolled in both an English and an Algebra class?

(1) 20 are enrolled in exactly one of these two classes.

(2) 3 are not enrolled in either of these classes.

i can result to B. only St. 2 is sufficient, 30-3=27,8+16+24; 27-24, therefore 3 must be studying both..your take guyz...

Preet
The question is flawed. What's the source?

On the GMAT, language is very specific. When we see the phrase "8 are enrolled in an English class", we know nothing else about those people. For example, some of them could also be enrolled in the Algebra class.

Accordingly, statement (2) is impossible. If there are 30 students total, and 8 are in English and 16 in Algebra, then there must be at least 6 people (30 - 24) who aren't enrolled in either class.

If the question stem read "8 are enrolled only in an English class and 16 are enrolled only in an Algebra class", then (2) would make sense (and be sufficient).
Interesting, I had a side question Stuart. Please refer attached file what I did per the stem of the questions is make the following 3 equations:
X + Z = 8
Y +Z = 16
X + Y +Z + N = 30

And then went with the stmts, 1 gives me the 4th eqtn and so does stmt 2. Hence, I chose the answer D without solving fully (where I would have found the error in the question) to save time.

On the GMAT - is the above strategy correct or should I solve the question fully just to be sure?
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by Stuart@KaplanGMAT » Fri Jun 18, 2010 8:20 pm
mj78ind wrote:Interesting, I had a side question Stuart. Please refer attached file what I did per the stem of the questions is make the following 3 equations:
X + Z = 8
Y +Z = 16
X + Y +Z + N = 30

And then went with the stmts, 1 gives me the 4th eqtn and so does stmt 2. Hence, I chose the answer D without solving fully (where I would have found the error in the question) to save time.

On the GMAT - is the above strategy correct or should I solve the question fully just to be sure?
On the GMAT, you don't have to worry about flawed questions - so your methodology would be just fine.
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