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by DavidG@VeritasPrep » Fri Mar 04, 2016 5:44 am
sandipgumtya wrote:Somebody plz help me understand the prob here.[/img]
We can see pretty quickly that each statement alone is not sufficient. S1 gives no info about the number of students. S2 gives no info about the number employed.

Together we know the following: If there are 24 students, there are 18 who are not students. If there are 29 who are employed, there are 13 who are not employed. The problem is that there's no way to know what the overlap is between the pool of students and the pool of employed people. Are all 24 students employed? 23 students? 22? There's no way to know. So even together, the statements are not sufficient. Answer is E

In a matrix, you'd have the following:
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by Brent@GMATPrepNow » Fri Mar 04, 2016 7:41 am
I thought I'd point out that David's approach (Double Matrix Method) can be used for most questions featuring a population in which each member has two characteristics associated with it.
Here, we have a population of students, and the two characteristics are:
- employed or not employed
- student or not a student

This question type is VERY COMMON on the GMAT, so be sure to master the technique.

To learn more about the Double Matrix Method, watch our free video: https://www.gmatprepnow.com/module/gmat- ... ems?id=919

Once you're familiar with this technique, you can attempt these additional practice questions:

Easy Problem Solving questions
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Difficult Problem Solving questions
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- https://www.beatthegmat.com/ratio-problem-t268339.html
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Easy Data Sufficiency questions
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Medium Data Sufficiency questions
- https://www.beatthegmat.com/sets-matrix-ds-t271914.html
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Difficult Data Sufficiency questions
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- https://www.beatthegmat.com/double-set-m ... 71423.html
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- https://www.beatthegmat.com/mba/2011/05/ ... question-3

Cheers,
Brent
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by Matt@VeritasPrep » Fri Mar 04, 2016 3:23 pm
Another idea:

Suppose a people are employed non-students, b people are unemployed students, and c people are employed students.

We know that

a + c = 29
b + c = 24

But we can't solve for c, because we have three variables and only two equations.
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by sandipgumtya » Sun Mar 06, 2016 7:35 pm
Hi,
I was trying to solve this with venn diagram.I don't where i went wrong.Can we solve this prob using venn diagram also?which method is quicker?Pl explain.

Sandip.
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by ceilidh.erickson » Mon Mar 07, 2016 8:47 am
Yes, you can use a Venn diagram here. One very important issue to consider, though, is the space outside of the diagram: that is, those who are neither students nor employed. The problem doesn't tell us anything about that group, but we cannot assume that it doesn't exist. Thus, you need to create a bubble outside of the diagram for that group:
Image

We're looking for the number of people that are BOTH students and employed:

Image

As Matt said, the easiest thing to do once you've visualized this in a diagram is to assign variables. We actually have FOUR variables here, though, not three: S for "student only," E for "employed only," B both "both employed and a student," and N for "neither employed nor a student."

Image

So, S + B + E + N = 42

(1) tells us that B + E = 29. This is not sufficient to solve for B.

(2) tells us that S + B = 24. Again, not sufficient.

If we combine both statements, we still only have 3 equations, but we have 4 variables. Insufficient.

In cases in which there is a "neither" option, I think it's much easier to use the Double Set Matrix, which naturally contains those 4 options, and the additive relationships. Venn diagrams are helpful visual aids, but they are sometimes harder to construct equations with.
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by Matt@VeritasPrep » Thu Mar 17, 2016 9:05 pm
sandipgumtya wrote:Hi,
I was trying to solve this with venn diagram.I don't where i went wrong.Can we solve this prob using venn diagram also?which method is quicker?Pl explain.

Sandip.
You can, but one common problem students have with the Venn diagram is how easy it is to forget the 'other' group: the people who aren't in EITHER circle. If you forget this group, you naturally assume that all 42 people are in one group or the other, and find a solution ... but it isn't the only one!
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