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Is x^2 equal to xy?
(1) x^2 – y^2 = (x + 5)(y - 5)
(2) x = y
Statement One Only:
x^2 – y^2 = (x + 5)(y - 5)
If y = 5, we have:
x^2 - 25 = (x + 5)(0)
x^2 - 25 = 0
(x + 5)(x - 5) = 0
x = 5 or x = -5
If x = 5, then x^2 and xy will be equal since both are 25. However, if x = -5, then x^2 and xy will not be equal since the former is 25 and the latter is -25. Statement one alone is not sufficient.
Statement Two Only:
x = y
Since x = y, if we multiply both sides by x, we have:
x * x = y * x
x^2 = xy
Statement two alone is sufficient.
Answer: B
How have we arrived at y = 5?
It’s not
necessary for y to be 5 to satisfy x^2 – y^2 = (x + 5)(y - 5); it could take infinitely many other values. However, y
could be 5. If we assume y = 5, we find that x can be either 5 or -5, resulting in two different values for xy. Therefore, identifying a
possible value for y (such as y = 5) shows that this statement alone is insufficient.
Hope it's clear.
P.S. Pure algebraic questions are no longer a part of the
DS syllabus of the GMAT.
DS questions in GMAT Focus encompass various types of word problems, such as:
- Word Problems
- Work Problems
- Distance Problems
- Mixture Problems
- Percent and Interest Problems
- Overlapping Sets Problems
- Statistics Problems
- Combination and Probability Problems
While these questions may involve or necessitate knowledge of algebra, arithmetic, inequalities, etc., they will always be presented in the form of word problems. You won’t encounter pure "algebra" questions like, "Is x > y?" or "A positive integer n has two prime factors..."
Check
GMAT Syllabus for Focus EditionYou can also visit the
Data Sufficiency forum and filter questions by
OG 2024-2025, GMAT Prep (Focus), and Data Insights Review 2024-2025 sources to see the types of questions currently tested on the GMAT.
So, you can ignore this question.Hope it helps.