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If x - y = 5 and (x + 1)(y - 1) = 5, what is the value of xy?

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If x - y = 5 and (x + 1)(y - 1) = 5, what is the value of xy?

by Brent@GMATPrepNow » Sat Jul 02, 2022 5:28 am

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If x - y = 5 and (x + 1)(y - 1) = 5, what is the value of xy?
(A) -1
(B) 1
(C) 5
(D) 10
(E) 11

Answer: E
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GMAT/MBA Expert

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Posts: 16207
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Re: If x - y = 5 and (x + 1)(y - 1) = 5, what is the value of xy?

by Brent@GMATPrepNow » Mon Jul 04, 2022 8:12 am
Brent@GMATPrepNow wrote: ↑
Sat Jul 02, 2022 5:28 am
 If x - y = 5 and (x + 1)(y - 1) = 5, what is the value of xy?
(A) -1
(B) 1
(C) 5
(D) 10
(E) 11

Answer: E
Source: www.gmatprepnow.com
Given: (x + 1)(y - 1) = 5
Expand and simplify the left side: xy - x + y - 1 = 5
Add 1 to both sides of the equation: xy - x + y = 6
Add x and subtract y from both sides: xy = 6 + x - y
Substitute: xy = 6 + 5
Simplify: xy = 11

Answer: E
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