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Source: — Data Sufficiency |

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by [email protected] » Thu May 26, 2016 10:17 pm
HI amina.shaikh309,

This DS question can be solved by TESTing VALUES.

We're asked if the number of members of Club X is greater than the number of members of Club Y? This is a YES/NO question. In these sorts of situations, it's common for some members to belong to BOTH Clubs, so we have to keep careful track of the numbers and possibilities....

Fact 1: 20% of the members of Club X are ALSO members of Club Y

IF...
Club X has 100 members, then 20 of those members ALSO belong to Club Y.
IF Club Y has 0 unique members, then the answer to the question is YES.
IF Club Y as 1,000 unique members, then the answer to the question is NO.
Fact 1 is INSUFFICIENT

Fact 2: 30% of the members of Club Y are ALSO members of Club X

This Fact offers the same general logic as Fact 1 (above). Without knowing the number of unique members in Club X, the answer to the question could be either YES or NO.
Fact 2 is INSUFFICIENT

Combined, we know...
20% of the members of Club X are ALSO members of Club Y
30% of the members of Club Y are ALSO members of Club X
These specific members are the SAME PEOPLE...

This means that .2(X) = .3(Y)

2X = 3Y
X = (3/2)(Y)

This means that X MUST be greater than Y, so the answer to the question is ALWAYS YES.
Combined, SUFFICIENT

Final Answer: C

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Rich
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by MartyMurray » Thu May 26, 2016 10:18 pm
amina.shaikh309 wrote:Is the number of members of Club X greater than the number of members of Club Y?

(1) Of the members of Club X, 20 percent are also members of Club Y.

(2) Of the members of Club Y, 30 percent are also members of Club X.
Notice: The members of a club cannot be a negative number.

Statement 1:

All this tells us is that of the members of Club X 20% are also members of Club Y.

Club X could have 10 members, 2 of which are members of Club Y, and Club Y could have 100 members.

Answer To The Question: No.

Club X could have 10 members, 2 of which are members of Club Y, and Club Y could have 2 members.

Answer To The Question: Yes.

Insufficient.

Statement 2:

This is almost a mirror image of Statement 1 and similarly supports both a Yes answer and a No answer to the question.

Insufficient.

Statements Combined:

20% of Club X are in both Club X and Club Y.

30% of Club Y are in both Club X and Club Y.

The 20% of Club X and the 30% of Club Y are the same group of people, the people in both clubs.

So the same number is 20% of Club X but 30% of Club Y, meaning the same number represents a greater percentage of Club Y than of Club X. So Club Y must be smaller.

Mathematically, .2OX = .30Y. So X/Y = 3/2. Since X and Y cannot be negative, X must be greater.

Sufficient.

The correct answer is C.
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by Matt@VeritasPrep » Fri May 27, 2016 2:25 pm
Let's say that x people belong only to Club X, y belong only to Club Y, and z belong to both.

S1:

z = .2x

Doesn't tell us about y; NOT SUFFICIENT

S2:

z = .3y

Doesn't tell us about x; NOT SUFFICIENT

S1 + S2:

z = .2x = .3y

.2x = .3y

x = (.3/.2)y

x = 1.5y

So x > y, and we're set!
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by nchaswal » Sat May 28, 2016 5:33 am
Dear Amina

This question was hardly a 40 sec question. You just need to focus on key values and hardly have to do any algebra or calculation if the fundamentals are clear.

The key point to note from question stem are:-

a) The question is asking for a specific VALUE
b) %ages are never conclusive

If you remember both points, you would save extra thinking in many problems which involve %ages

Statement 1: INSUFFICIENT (15 Secs)

You even do not have to think TWICE to check this statement is sufficient or not. Giving % are almost always sure way for INSUFFICIENT when you are talking about actual values.

Statement 2: INSUFFICIENT (5 Secs due to same reasoning above)

Same reasoning.

COMBINE: SUFFICIENT (10 secs)

Here too you do not have to think more than 15-20 secs or even lesser as you know two facts & those two facts are same. Therefore you CAN solve for the value that which (X or Y) is larger. Irrespective of which is larger you should just note that you already have all the tools to find the answer and THATS IT. STOP THERE.

Select C and move on. Hardly 40-45 secs problem.

Remember the objective is not just to get the question right BUT how to get the question right SMARTLY. Every second you save in your thinking or calculation will give u results later when you will hit on a hard problem.

Cheers
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by Matt@VeritasPrep » Tue Jun 07, 2016 11:52 pm
nchaswal wrote:Irrespective of which is larger you should just note that you already have all the tools to find the answer and THATS IT. STOP THERE.
Nicely explained, nchaswal! I hope you get that 760: you've got a future in test preparation :)
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by nchaswal » Wed Jun 08, 2016 12:14 am
Matt@VeritasPrep wrote:
nchaswal wrote:Irrespective of which is larger you should just note that you already have all the tools to find the answer and THATS IT. STOP THERE.
Nicely explained, nchaswal! I hope you get that 760: you've got a future in test preparation :)
Thank you Matt for your generous comments and wishes. But CR is my nemesis which won't let me achieve 760. For CR my accuracy levels are just 50-60% sadly. :|. Have to really work a lot on that..
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by Matt@VeritasPrep » Fri Jun 10, 2016 10:08 am
nchaswal wrote:
Matt@VeritasPrep wrote:
nchaswal wrote:Irrespective of which is larger you should just note that you already have all the tools to find the answer and THATS IT. STOP THERE.
Nicely explained, nchaswal! I hope you get that 760: you've got a future in test preparation :)
Thank you Matt for your generous comments and wishes. But CR is my nemesis which won't let me achieve 760. For CR my accuracy levels are just 50-60% sadly. :|. Have to really work a lot on that..
If that's the one topic that's really troubling you, I might take a look at some old LSAT exams and some LSAT prep material. CR (which the LSAT calls Logical Reasoning) is about 40% of that test, so there's a lot more of it to practice, at more difficulty levels, but the types are essentially the same as what you'll encounter on the GMAT: Strengthen, Weaken, Inference, Assumption, etc. The crucial thing is that there's a lot of it and that it's well-edited and well-explained.
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