For a certain exam, was the standard deviation of the scores

[rakeshd347]

For a certain exam, was the standard deviation of the scores for students U, V, W, X, Y, Z less than the standard deviation of the scores for students A B and C?

1. The standard deviation of the scores of students U V and W was less than the standard deviation of the scores of the students A B and C on the exam

2. The standard deviation of the scores of students X Y and Z was less than the standard deviation of the scores of the students A B and C on the exam

OA coming soon.

[theCodeToGMAT]

To find : SD (A,B,C) < SD (U,V,W,X,Y,Z)

We don't know whether the scores are in AP or not.. So the scores could be spread widely...

Statement 1:
SD(U,V,W) < SD (A,B,C)
--> U,V,W are closer to mean than A,B,C.. but we don't know values.. the others can have any value
INSUFFiCIENT

Statement 2:
SD(X,Y,Z) < SD (A,B,C)
--> X,Y,Z are closer to mean than A,B,C.. but we don't know values.. the others can have any value
INSUFFICIENT

Combining,

Assuming the score order is U,V,W,X,Y,Z
there are two possibilities.. either W & X are close to each other.. then SD of (A,B,c) would be higher..

BUT, if they are not close to each other.. say W=30 & X=90.. then mean would be impacted.. and hence SD would increase.

INSUFFICIENT

Answer [spoiler]{E}[/spoiler]

What is the OA??

[Brent@GMATPrepNow]

For a certain exam, was the standard deviation of the scores for students U, V, W, X, Y, Z less than the standard deviation of the scores for students A B and C?

1. The standard deviation of the scores of students U V and W was less than the standard deviation of the scores of the students A B and C on the exam

2. The standard deviation of the scores of students X Y and Z was less than the standard deviation of the scores of the students A B and C on the exam

For this question, we can use the fact that when all values are equal, the standard deviation = 0.

Target question: Was the standard deviation of the scores for students U, V, W, X, Y, Z less than the standard deviation of the scores for students A B and C?

Statement 1: The standard deviation of the scores of students U V and W was less than the standard deviation of the scores of the students A B and C on the exam
There are several sets of scores that satisfy this condition. Here are two:
Case a: U = V = W = 0, X = Y = Z = 100, and A = 1, B = 2, C = 3. In this case, the standard deviation of U, V, W, X, Y, Z greater than the standard deviation of A B and C.
Case b: U = V = W = X = Y = Z = 100, and A = 1, B = 2, C = 3. In this case, the standard deviation of U, V, W, X, Y, Z less than the standard deviation of A B and C.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: The standard deviation of the scores of students X Y and Z was less than the standard deviation of the scores of the students A B and C on the exam
There are several sets of scores that satisfy this condition. Here are two:
Case a: U = V = W = 0, X = Y = Z = 100, and A = 1, B = 2, C = 3. In this case, the standard deviation of U, V, W, X, Y, Z greater than the standard deviation of A B and C.
Case b: U = V = W = X = Y = Z = 100, and A = 1, B = 2, C = 3. In this case, the standard deviation of U, V, W, X, Y, Z less than the standard deviation of A B and C.
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
There are still several sets of scores that satisfy this condition. Here are two:
Case a: U = V = W = 0, X = Y = Z = 100, and A = 1, B = 2, C = 3. In this case, the standard deviation of U, V, W, X, Y, Z greater than the standard deviation of A B and C.
Case b: U = V = W = X = Y = Z = 100, and A = 1, B = 2, C = 3. In this case, the standard deviation of U, V, W, X, Y, Z less than the standard deviation of A B and C.
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer = E

Cheers,
Brent