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What percent of members take yoga classes?

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by gmattesttaker2 » Sun May 04, 2014 8:54 pm
Hello,

Can you please tell me where I am going wrong here. This is from Veritas practice test.

A certain health club offers only yoga classes and spin classes. If all club members take at least one type of class, what percent of members take yoga classes?

(1) 30% of members take both types of classes.

(2) 40% of members take only spin classes.


OA: B


Let total members be n. Let members taking yoga be y and spin be s

y = (?/100) (n)

1) 30/100(n) = y + s - In-suff.

2) 40/100(n) = s - In-suff.


I selected E but it's obviously wrong.


The explanation talks about using Venn diagrams.

I tried to use a double set matrix but then I still don't know the total number of members here. Can you please assist?

Thanks a lot,
Sri
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Source: — Data Sufficiency |

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by Brent@GMATPrepNow » Sun May 04, 2014 9:46 pm
A certain health club offers only yoga classes and spin classes. If all club members take at least one type of class, what percent of members take yoga classes?

(1) 30% of members take both types of classes.
(2) 40% of members take only spin classes.
The 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 health club members, and the two characteristics are:
- taking yoga or not taking yoga
- taking spin classes or not taking spin classes

So, we can set up our diagram as follows:
Image
IMPORTANT: Notice that I placed a zero in the bottom right corner because we are told that all club members take at least one type of class
In other words, there are zero members who take neither yoga nor spin classes.

Also notice that I made the total population of club members = 100. This is okay since the target question asks us to find a certain PERCENT.

Target question: What percent of members take yoga classes?

In other words, we want to find the sum of the top two boxes.
Image

Statement 1: 30% of members take both types of classes.
So, we can place 30 of the 100 members in the top-left box.
Image
Does this provide enough information to find the sum of the top two boxes?
No.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: 40% of members take only spin classes.
So, we can place a 40 in the bottom left box.
Image

This means that a total of 40 of the 100 members do NOT take yoga.
Image

From this, we can conclude that the remaining 60 members DO take yoga.
Image
In other words, 60% of the members take yoga.
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer = B
-------------------------------------

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:

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- https://www.beatthegmat.com/double-set-m ... 71423.html
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Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by gmattesttaker2 » Sun May 04, 2014 10:48 pm
Brent@GMATPrepNow wrote:
A certain health club offers only yoga classes and spin classes. If all club members take at least one type of class, what percent of members take yoga classes?

(1) 30% of members take both types of classes.
(2) 40% of members take only spin classes.
The 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 health club members, and the two characteristics are:
- taking yoga or not taking yoga
- taking spin classes or not taking spin classes

So, we can set up our diagram as follows:
Image
IMPORTANT: Notice that I placed a zero in the bottom right corner because we are told that all club members take at least one type of class
In other words, there are zero members who take neither yoga nor spin classes.

Also notice that I made the total population of club members = 100. This is okay since the target question asks us to find a certain PERCENT.

Target question: What percent of members take yoga classes?

In other words, we want to find the sum of the top two boxes.
Image

Statement 1: 30% of members take both types of classes.
So, we can place 30 of the 100 members in the top-left box.
Image
Does this provide enough information to find the sum of the top two boxes?
No.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: 40% of members take only spin classes.
So, we can place a 40 in the bottom left box.
Image

This means that a total of 40 of the 100 members do NOT take yoga.
Image

From this, we can conclude that the remaining 60 members DO take yoga.
Image
In other words, 60% of the members take yoga.
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer = B
-------------------------------------

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
- https://www.beatthegmat.com/the-aam-aadm ... 72242.html
- https://www.beatthegmat.com/finance-majo ... 67425.html

Medium Problem Solving questions
- https://www.beatthegmat.com/probability- ... 73360.html
- https://www.beatthegmat.com/posted-speed ... 72374.html
- https://www.beatthegmat.com/motel-t271938.html
- https://www.beatthegmat.com/of-the-appli ... 70255.html
- https://www.beatthegmat.com/opening-nigh ... 64869.html
- https://www.beatthegmat.com/ds-french-ja ... 22297.html

Difficult Problem Solving questions
- https://www.beatthegmat.com/ratio-problem-t268339.html
- https://www.beatthegmat.com/overlapping- ... 65223.html
- https://www.beatthegmat.com/fractions-t264254.html
- https://www.beatthegmat.com/overlapping- ... 64092.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-2

Easy Data Sufficiency questions
- https://www.beatthegmat.com/for-what-per ... 70596.html
- https://www.beatthegmat.com/ds-quest-t187706.html

Medium Data Sufficiency questions
- https://www.beatthegmat.com/sets-matrix-ds-t271914.html
- https://www.beatthegmat.com/each-of-peop ... 71375.html
- https://www.beatthegmat.com/a-manufacturer-t270331.html
- https://www.beatthegmat.com/in-costume-f ... 69355.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-1

Difficult Data Sufficiency questions
- https://www.beatthegmat.com/double-set-m ... 71423.html
- https://www.beatthegmat.com/sets-t269449.html
- https://www.beatthegmat.com/mba/2011/05/ ... question-3

Cheers,
Brent

Hello Brent,

Thanks a lot for the excellent explanation.

Best Regards,
Sri
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by [email protected] » Sun May 04, 2014 11:43 pm
Hi Sri,

Certain DS questions appear far more complex than they actually are.

In this DS prompt, we're told that there are 3 types of people:

1) Those who take JUST yoga classes
2) Those who take JUST spin classes
3) Those who take BOTH classes.

We're asked what percent of member take yoga classes. To answer this question, we'll need to know...
1) what percent make up groups 1 and 3
OR
2) what percent make up group 2 (then we'll know that EVERYONE ELSE takes yoga classes)

Fact 1: 30% of member take BOTH classes.

This gives us info on just group 3, which is not enough to answer the question.
Fact 1 is INSUFFICIENT

Fact 2: 40% of members take ONLY spin classes.

This tells us about group 2. By extension, everyone else MUST take a yoga class (that's 60% of members).
Fact 2 is SUFFICIENT

Final Answer: B

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
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