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Bunuel

200 people responded to a survey that asked them to rank three different brands of soap. The percentage of respondents that ranked each brand 1st, 2nd, and 3rd are listed above. If no respondents rated the soaps in the order Y, Z, X, how many respondents rated the soap in the following order: X, Y, Z?

A. 100
B. 60
C. 50
D. 30
E. 25

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Attachment:
Brand_Rankings.png

VERITAS PREP OFFICIAL SOLUTION:

In a way this problem is a permutations problem in disguise. When you're given the caveat that no one responded in the order Y, Z, X, you can tell a few things:

Anyone who put Y first did so in the order Y, X, Z (because there are only two ways to arrange X and Z if Y is in the first spot, and one of those was expressly prohibited by the prompt).

And, similarly, anytime that Z was second the order was X, Z, Y (because Y and Z couldn't have been arranged in the other order with Z fixed in the middle); and anytime X was last the order had to be Z, Y, X (because the other "X third" option is prohibited).

So if you follow that logic, your next step is to pick one of those certainties (for example, for all 60 cases of Y first - Y was first in 30% of the 200 cases - the order was Y, X, Z) and incorporate the statistics. That means that of the 110 cases of Z going last, 60 of them were in the order Y, X, Z. Which then means that, since the only other way to fix Z at the last spot is to go in the asked-about order X, Y, Z, the other 50 cases of Z third have to have come from the X, Y, Z order. Therefore, the answer is 50.
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I felt dumb, I couldn t get how you infer "people who ranked Y number 1 = 30% of 200 = 60." from the graphs? maybe cause it's late here
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faltan
I felt dumb, I couldn t get how you infer "people who ranked Y number 1 = 30% of 200 = 60." from the graphs? maybe cause it's late here

Question states:
200 people responded to a survey that asked them to rank three different brands of soap. The percentage of respondents that ranked each brand 1st, 2nd, and 3rd are listed above.
If no respondents rated the soaps in the order Y, Z, X, how many respondents rated the soap in the following order: X, Y, Z?

Given:
The first graph tells up how many people rated each brand of soap number 1:
40% rated X number 1. 30% rated Y number 1 and 30% rated Z number 1.

The second graph tells up how many people rated each brand of soap number 2:
45% rated X number 2. 40% rated Y number 2 and 15% rated Z number 2.

The third graph tells up how many people rated each brand of soap number 1:
15% rated X number 3. 30% rated Y number 3 and 55% rated Z number 3.

YZX = 0. ---- eq (1)

Calculations
15% = 30 people rated Z number 2. Possible combinations with Z in middle is XZY or YZX. So, 30 people voted for XZY because no respondents rated the soaps in the order Y, Z, X.
Basically,
XZY + YZX = 30 ,
From eq(1) we get XZY + 0 = 30 ,
XZY = 30 --- eq (2)

40% = 80 people rated X number 1. These people voted for XYZ or XZY .
Basically,
XYZ + XZY = 80.
From eq (2), we get XZY = 30 .
XYZ + 30 = 80.
So, XYZ = 50.
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Mike03
A very good question. Here is my approach:

Order of choices people can make -

X Y Z
X Z Y
Y X Z
Y Z X = 0 people made this choice
Z X Y
Z Y X

People who ranked X number 1 = 40% of 200 = 80. This implies that the sum of X Y Z & X Z Y is equal to 80.

People who ranked Y number 1 = 30% of 200 = 60. This implies that the sum of Y X Z & Y Z X is equal to 60. Since Y Z X is 0, this implies that the number of people who picked the order Y X Z is 60.

People who ranked Z number 3 = 55% of 200 = 110. This implies that the sum of Y X Z & X Y Z is equal to 110. Since Y X Z is 60, this implies that X Y Z =50. Therefore, the correct answer is C.

Hi Mike03, How is 'People who ranked Z number 3 = 55% of 200 = 110'?
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Bunuel

200 people responded to a survey that asked them to rank three different brands of soap. The percentage of respondents that ranked each brand 1st, 2nd, and 3rd are listed above. If no respondents rated the soaps in the order Y, Z, X, how many respondents rated the soap in the following order: X, Y, Z?

A. 100
B. 60
C. 50
D. 30
E. 25

Kudos for a correct solution.

Attachment:
Brand_Rankings.png


There was no YZX order. So who are the 15% people who rated X last? (from fig 3)
They must have rated ZYX (nothing else is possible). So 15% people rated ZYX.

Now, who are the 40% people who rated Y in the middle? (from fig 2) They are those who rated XYZ and ZYX (nothing else is possible). We know that 15% people rated ZYX. Then rest 25% must have rated XYZ. 25% gives us 50 people.
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Question asks for how many made the choice X Y Z. The total combos are:
I) X Y Z = The unknown we need to find.
II) X Z Y
III) Y Z X = 0 (Given in stem)
IV) Y X Z
V) Z X Y
VI) Z Y X

we know, by looking at the graphs, that those who put X first (I + II) is 40% = 80 people (40% of 200) - Using graph first choice. But we need to know what is the value of I only, without the addition of II. How to find this? Well, we know that those who put Z second consists of II and III, and III is zero, so the 15% (graph 2nd choice) who put Z second consists only of II as III = 0, so II = 0.15*200 = 30. Thus: (I + II) - (II) = I = X Y Z = 80 - 30 = 50.
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