As advertised on the main page of Beat the GMAT, Ashley, David, and I will be posting some original questions today and tomorrow with prizes for the first five students to respond with correct answers that show your work!
Here's a Data Sufficiency question to kick things off. I love multiple variables and exponents...
What is the value of x - y?
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
(For more information on the contest, please visit https://www.beatthegmat.com/mba/2011/07/ ... g-tomorrow, and note that the "tomorrow" in the URL was posted yesterday, making the date in question "today"!)
Veritas Prep Challenge Question
- Brian@VeritasPrep
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Brian Galvin
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Veritas Prep
Looking for GMAT practice questions? Try out the Veritas Prep Question Bank. Learn More.
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Veritas Prep
Looking for GMAT practice questions? Try out the Veritas Prep Question Bank. Learn More.
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Hi,
From(1):
x^2+y^2+2xy = 4xy
So, x^2+y^2-2xy = 0
So, (x-y)^2 =0 =>x-y = 0
Sufficient
From(2):
(x+y)(x-y) = 0
So, either x+y = 0 or x-y =0 or both are equal to zero
Not sufficient to find the value of (x-y)
Hence, A
From(1):
x^2+y^2+2xy = 4xy
So, x^2+y^2-2xy = 0
So, (x-y)^2 =0 =>x-y = 0
Sufficient
From(2):
(x+y)(x-y) = 0
So, either x+y = 0 or x-y =0 or both are equal to zero
Not sufficient to find the value of (x-y)
Hence, A
Cheers!
Things are not what they appear to be... nor are they otherwise
Things are not what they appear to be... nor are they otherwise
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(x+y)^2 -4xy = (x-y)^2
=> from statement 1
(x+y)^2 = 4xy
we get (x-y)^2 =0
so x-y = 0
=> Statement 2
x^2- y^2 =
(x+y)(x-y) = 0
so either x+y = 0 or x-y =0
so this is insufficient
SO A should be correct
=> from statement 1
(x+y)^2 = 4xy
we get (x-y)^2 =0
so x-y = 0
=> Statement 2
x^2- y^2 =
(x+y)(x-y) = 0
so either x+y = 0 or x-y =0
so this is insufficient
SO A should be correct
Dear life , When I said "Can my day get any worse" It was a rhetorical question not a challenge!
What is the value of x - y?
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
Answer: (A)
Statement 1:
(x+y)^2 = 4xy
--> x^2 + 2xy + y^2 = 4xy
--> x^2 + y^2 = 2xy
--> x^2 - 2xy +y^2 = 0
--> (x-y)^2 = 0
--> (x-y) = 0
Stmnt 1: Sufficient
Statement 2:
x^2 - y^2 = 0
--> (x+y)*(x-y) = 0
--> Either term could be equal to zero.
Stmnt 2: Insufficient
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
Answer: (A)
Statement 1:
(x+y)^2 = 4xy
--> x^2 + 2xy + y^2 = 4xy
--> x^2 + y^2 = 2xy
--> x^2 - 2xy +y^2 = 0
--> (x-y)^2 = 0
--> (x-y) = 0
Stmnt 1: Sufficient
Statement 2:
x^2 - y^2 = 0
--> (x+y)*(x-y) = 0
--> Either term could be equal to zero.
Stmnt 2: Insufficient
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Answer is A
What is the value of x - y?
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
x2 + y2 + 2xy=4xy
x2 + y2 -2xy=0
(x-y)2=0
x-y=0
2)Insufficient
x2-y2=0
x-y)(x+y)=0
x+y could be 0 .In this case x-y=-2y=2x or x-y could be 0 thus Insufficient
So A Alone is sufficient
What is the value of x - y?
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
x2 + y2 + 2xy=4xy
x2 + y2 -2xy=0
(x-y)2=0
x-y=0
2)Insufficient
x2-y2=0
x-y)(x+y)=0
x+y could be 0 .In this case x-y=-2y=2x or x-y could be 0 thus Insufficient
So A Alone is sufficient
I Seek Explanations Not Answers
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What is the value of x - y?
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
Statement 1) gives x^2+y^2+2xy-4xy=0
or, (x-y)^2=0
Hence, x-y can only be zero and hence sufficient
Statement 2) gives (x-y)*(x+y)=0
implying either x-y=0 or x+y=0
So,x-y cant be determined
Insufficient
Answer A
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
Statement 1) gives x^2+y^2+2xy-4xy=0
or, (x-y)^2=0
Hence, x-y can only be zero and hence sufficient
Statement 2) gives (x-y)*(x+y)=0
implying either x-y=0 or x+y=0
So,x-y cant be determined
Insufficient
Answer A
- jainnikhil02
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A is the correct answer
I know its very easy but explanation is same as mentioned above.
I know its very easy but explanation is same as mentioned above.
Nikhil K Jain
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"Life is all about timing" Don't waste your and others time.
____________________
"Life is all about timing" Don't waste your and others time.
What is the value of x - y?
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
we are asked to find the difference between x and y. To find the diff., we do not necessarily need to know the individual values of x and y.
Statement 1: (x + y)^2 = 4xy, by expanding the equation, we get
x^2 + y^2 + 2xy = 4xy, taking 4xy to left hand side,
x^2 + y^2 - 2xy = 0
(x - y)^2 = 0
x - y = 0
Statement 1 is sufficient. eliminate B, C and E. The correct answer answer choice is A or D.
Statement 2 x^2 - y^2 = 0 can be rewritten as (x + y)(x - y) = 0, however we can't simplify the equation further to get the unique value of x - y as either x + y can be zero or x - y can be zero. Therefore, Statement 2 alone is NOT sufficient.
Answer Choice A is correct.
1) (x + y)^2 = 4xy
2) x^2 - y^2 = 0
we are asked to find the difference between x and y. To find the diff., we do not necessarily need to know the individual values of x and y.
Statement 1: (x + y)^2 = 4xy, by expanding the equation, we get
x^2 + y^2 + 2xy = 4xy, taking 4xy to left hand side,
x^2 + y^2 - 2xy = 0
(x - y)^2 = 0
x - y = 0
Statement 1 is sufficient. eliminate B, C and E. The correct answer answer choice is A or D.
Statement 2 x^2 - y^2 = 0 can be rewritten as (x + y)(x - y) = 0, however we can't simplify the equation further to get the unique value of x - y as either x + y can be zero or x - y can be zero. Therefore, Statement 2 alone is NOT sufficient.
Answer Choice A is correct.
From Statement (1) we have:
(x+y)^2 = 4xy
So, x^2+y^2+2xy = 4xy
So, x^2+y^2-2xy = 0
So, (x-y)^2 =0 =>x-y = 0
So, Statement 1 is Sufficient
From Statement (2) we have:
(x^2 - y^2)=0
So,(x+y)(x-y) = 0
So, Either x+y = 0 or x-y =0 or both are equal to zero
So, Not sufficient to find the value of (x-y)
Hence, the answer is A
(x+y)^2 = 4xy
So, x^2+y^2+2xy = 4xy
So, x^2+y^2-2xy = 0
So, (x-y)^2 =0 =>x-y = 0
So, Statement 1 is Sufficient
From Statement (2) we have:
(x^2 - y^2)=0
So,(x+y)(x-y) = 0
So, Either x+y = 0 or x-y =0 or both are equal to zero
So, Not sufficient to find the value of (x-y)
Hence, the answer is A
- amit2k9
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a x^2-2xy+y^2 = 0
means (x-y)^2 = 0 or x-y = 0 meaning x=y.
b either x+y or x-y = 0. not sufficient.
hence A it is.
means (x-y)^2 = 0 or x-y = 0 meaning x=y.
b either x+y or x-y = 0. not sufficient.
hence A it is.
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- Brian@VeritasPrep
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Great work, everyone - the correct answer is, indeed, A.
Statement 1, when you break out the parentheses, looks like:
x^2 + 2xy + y^2 = 4xy
And can be reset into the ax^2 + bx + c quadratic form by subtracting 4xy from both sides to get:
x^2 - 2xy + y^2 = 0
You should recognize this as a fairly common algebraic equation - it's the same as:
(x - y)^2 = 0
Which means that x - y = 0 --> the statement is sufficient as it gives us a definite answer to the question.
Statement 2 gets us a step closer if we apply the Difference of Squares factor:
(x + y)(x - y) = 0
We know that either x + y = 0 or x - y = 0, but we don't know which one, so statement 2 is not sufficient, and the correct answer is A.
I like this question because statement 1 rewards you for recognizing the common algebraic transformations between the factored (x+y)^2 and expanded (x^2 + 2xy + y^2) displays of the same equation. Data Sufficiency questions that employ algebra often reward you for changing the view of the same statement - I call this "an inconvenient truth", in which the test gives you a statement in an inconvenient form, and you need to transform it to look more like what the question is asking.
This question also has some further discussion that can make it more valuable. Can anyone think of a restriction that we could put on x and/or y that would make statement 2 sufficient?
Statement 1, when you break out the parentheses, looks like:
x^2 + 2xy + y^2 = 4xy
And can be reset into the ax^2 + bx + c quadratic form by subtracting 4xy from both sides to get:
x^2 - 2xy + y^2 = 0
You should recognize this as a fairly common algebraic equation - it's the same as:
(x - y)^2 = 0
Which means that x - y = 0 --> the statement is sufficient as it gives us a definite answer to the question.
Statement 2 gets us a step closer if we apply the Difference of Squares factor:
(x + y)(x - y) = 0
We know that either x + y = 0 or x - y = 0, but we don't know which one, so statement 2 is not sufficient, and the correct answer is A.
I like this question because statement 1 rewards you for recognizing the common algebraic transformations between the factored (x+y)^2 and expanded (x^2 + 2xy + y^2) displays of the same equation. Data Sufficiency questions that employ algebra often reward you for changing the view of the same statement - I call this "an inconvenient truth", in which the test gives you a statement in an inconvenient form, and you need to transform it to look more like what the question is asking.
This question also has some further discussion that can make it more valuable. Can anyone think of a restriction that we could put on x and/or y that would make statement 2 sufficient?
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
Looking for GMAT practice questions? Try out the Veritas Prep Question Bank. Learn More.
GMAT Instructor
Chief Academic Officer
Veritas Prep
Looking for GMAT practice questions? Try out the Veritas Prep Question Bank. Learn More.