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If x + y = 7 and x – y = 3, then x^2 - y^2 =
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16 Feb 2021, 05:38
16 Feb 2021, 05:38
Expert Reply
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Question Stats:
98% (00:25) correct
1% (00:18) wrong based on 54 sessions
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If x + y = 7 and x – y = 3, then \(x^2 - y^2 =\)
A. -4
B. 4
C. 10
D. 21
E. 40
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book
A. -4
B. 4
C. 10
D. 21
E. 40
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book
Re: If x + y = 7 and x – y = 3, then x^2 - y^2 =
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16 Feb 2021, 06:03
16 Feb 2021, 06:03
1
Hi,
This question is all about knowing formula:
(x+y)(x-y)=x^2-y^2
Substitute the values to get answer as 21.
IMO D
This question is all about knowing formula:
(x+y)(x-y)=x^2-y^2
Substitute the values to get answer as 21.
IMO D
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: If x + y = 7 and x – y = 3, then x^2 - y^2 =
[#permalink]
16 Feb 2021, 06:47
16 Feb 2021, 06:47
Carcass wrote:
If x + y = 7 and x – y = 3, then \(x^2 - y^2 =\)
A. -4
B. 4
C. 10
D. 21
E. 40
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book
A. -4
B. 4
C. 10
D. 21
E. 40
Kudos for the right answer and explanation
Question part of the project GRE Quantitative Reasoning Daily Challenge - (2021) EDITION
GRE - Math Book
The fastest approach (identifying the difference of squares) has already been shown by Ks1859.
So, 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
Cheers,
Brent
