Max@Math Revolution wrote:(x-y)² - (x+y)² = ?
1) xy = 5
2) x + y = 6
Target question: What is the value of (x-y)² - (x+y)² ?
This is an ideal candidate for REPHRASING the target question.
(x-y)² - (x+y)² = [x² - 2xy + y²] - [x² + 2xy + y²]
= -4xy
Great, this is a much easier expression.
REPHRASED target question: What is the value of -4xy ?
Statement 1: xy = 5
Perfect.
If xy = 5, then
-4xy = -4(5) = -20
Since we can answer the
REPHRASED target question with certainty, statement 1 is SUFFICIENT
Statement 2: x + y = 6
There are several values of x and y that satisfy statement 2. Here are two:
Case a: x = 0 and y = 6, in which case
-4xy = -4(0)(6) = 0
Case b: x = 1 and y = 5, in which case
-4xy = -4(1)(5) = -20
Since we cannot answer the
REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT
Answer =
A
RELATED VIDEOS:
- Rephrasing the target question:
https://www.gmatprepnow.com/module/gmat ... video/1100
- The FOIL method:
https://www.gmatprepnow.com/module/gmat ... /video/952
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
