A marketing firm determined that,of 200 households surveyed,80 used neither brand A nor brand B soap,60 used only brand A soap,and for every household that used both brands soap,3 used only brand B soap.How many of the 200 household surveyed used both brands soap?
A) 15
B) 20
c) 30
D) 40
E) 45
double matrix problem
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We can also solve this question using the Double Matrix Method.A marketing firm determined that, of 200 households surveyed, 80 used neither Brand A nor Brand B soap, 60 used only Brand A soap, and for every household that used both brands of soap, 3 used only Brand B soap. How many of the 200 households surveyed used both brands of soap?
A: 15
B: 20
C: 30
D: 40
E: 45
Here, we have a population of 200 households , and the two characteristics are:
- using or not using Brand A soap
- using or not using Brand B soap
So, we can set up our matrix as follows (where "~" represents "not"):
80 used neither Brand A nor Brand B soap
We can add this to our diagram as follows:
60 used only Brand A soap
We get...
At this point, we can see that the right-hand column adds to 140, which means 140 households do NOT use brand B soap.
Since there are 200 households altogether, we can conclude that 60 households DO use brand B soap.
For every household that used BOTH brands of soap...
Let's let x = # of households that use BOTH brands....
...3 used only Brand B soap.
So, 3x = # of households that use ONLY brand B soap
At this point, when we examine the left-hand column, we can see that x + 3x = 60
Simplify to get 4x = 60
Solve to get x = 15
How many of the 200 households surveyed used BOTH brands of soap?
Since x = # of households that use BOTH brands of soap, the correct answer here is A
------------------------------------
Overlapping sets questions are 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:
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Difficult Data Sufficiency questions
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Cheers,
Brent
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- Jay@ManhattanReview
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We know that 200 - 80 = 120 use ONLY A, ONLY B, and BOTH A & B.neha shekhawat wrote:A marketing firm determined that, of 200 households surveyed, 80 used neither brand A nor brand B soap, 60 used only brand A soap, and for every household that used both brands soap,3 used only brand B soap. How many of the 200 household surveyed used both brands soap?
A) 15
B) 20
c) 30
D) 40
E) 45
Thus, 120 = ONLY A + ONLY B + BOTH A & B
=> 120 = 60 + ONLY B + BOTH A & B
Say x households use BOTH A & B, thus, ONLY B households = 3*x = 3x
=> 60 = 3x + x
=> [spoiler]x = 15[/spoiler]
Relevant book: Manhattan Review GMAT Word Problems
Answer: A
Hope this helps!
-Jay
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GMAT/MBA Expert
- Jay@ManhattanReview
- GMAT Instructor
- Posts: 3008
- Joined: Mon Aug 22, 2016 6:19 am
- Location: Grand Central / New York
- Thanked: 470 times
- Followed by:34 members
We know that 200 - 80 = 120 use ONLY A, ONLY B, and BOTH A & B.neha shekhawat wrote:A marketing firm determined that, of 200 households surveyed, 80 used neither brand A nor brand B soap, 60 used only brand A soap, and for every household that used both brands soap,3 used only brand B soap. How many of the 200 household surveyed used both brands soap?
A) 15
B) 20
c) 30
D) 40
E) 45
Thus, 120 = ONLY A + ONLY B + BOTH A & B
=> 120 = 60 + ONLY B + BOTH A & B
Say x households use BOTH A & B, thus, ONLY B households = 3*x = 3x
=> 60 = 3x + x
=> [spoiler]x = 15[/spoiler]
Relevant book: Manhattan Review GMAT Word Problems
Answer: A
Hope this helps!
-Jay
_________________
Manhattan Review GMAT Prep
Locations: New York | Bangalore | Guangzhou | Buenos Aires | and many more...
Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.