Bunuel wrote:
If x + y = 7 and x – y = 3, then x² - y² =
A. -4
B. 4
C. 10
D. 21
E. 40
The fastest approach has already been shown. Here's one more option.
Given:
x + y = 7
x – y = 3
Add the two equations to get: 2x = 10, which means x = 5
If x = 5, we can plug that value into either equation, to conclude that y = 2
If x = 5 and y = 2, then x² - y² = 5² - 2² = 25 - 4 = 21
Answer: D
RELATED RESOURCES (free videos) FOR SOLVING THIS QUESTIONS- Solving 2 equations with 2 unknowns:
https://www.gmatprepnow.com/module/gmat ... /video/966 - Difference of square factoring:
https://www.gmatprepnow.com/module/gmat ... /video/955Cheers,
Brent
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