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In a chain of 40 restaurants

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by melguy » Mon Aug 19, 2013 4:39 am
Hello All

I tried this problem and the values in Statement 1 seem to fit in but I am a bit lost with how to enter the values of Statement 2 in the table.

Please help. Thanks
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by Brent@GMATPrepNow » Mon Aug 19, 2013 5:56 am
You're almost there!

Statement 2: 33 of the restaurants offer either a lunch menu or a dessert menu or both.
Which boxes in your diagram is this statement referring to?
It's referring to the entire top row (offers a dessert menu) as well as the left column (offers a lunch menu). So, the 3 boxes representing dessert+lunch, dessert+no-lunch, no-dessert+lunch must add to 33.
This means the last remaining box (no-dessert+no-lunch) must have 7 restaurants in it.

Answer = D

Aside: I should note that melguy's approach is known as the Double Matrix Method. This technique 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 restaurants, and the two characteristics are:
- dessert menu or no dessert menu
- offers lunch or doesn't offer lunch

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

Then try these additional practice questions that can be solved using the Double Matrix Method:
- https://www.beatthegmat.com/mba/2011/05/ ... question-1
- https://www.beatthegmat.com/mba/2011/05/ ... question-2
- https://www.beatthegmat.com/mba/2011/05/ ... question-3
- https://www.beatthegmat.com/ds-quest-t187706.html
- https://www.beatthegmat.com/overlapping- ... 83320.html
- https://www.beatthegmat.com/finance-majo ... 67425.html
- https://www.beatthegmat.com/ds-french-ja ... 22297.html

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by vt2net » Mon Aug 19, 2013 6:28 am
I think its easier, if you use Venn diagrams for these type of questions,
R -(L' ∩ U')=L ∪ U=L + U -(L ∩ U)
40-(L' ∩ U')=29 + 18 -(L ∩ U)
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by Brent@GMATPrepNow » Mon Aug 19, 2013 6:37 am
vt2net wrote:I think its easier, if you use Venn diagrams for these type of questions,
R -(L' ∩ U')=L ∪ U=L + U -(L ∩ U)
40-(L' ∩ U')=29 + 18 -(L ∩ U)
For easier questions, I think Venn diagrams and the Double Matrix Method work equally well.
However, for difficult questions involving variables (e.g., https://www.beatthegmat.com/mba/2011/05/ ... question-3), I think the Double Matrix Method is better for organizing information.

Cheers,
Brent
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