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# GRE Math Challenge #73- x^2 - 1 = y and x = 3

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GRE Math Challenge #73- x^2 - 1 = y and x = 3 [#permalink]  09 May 2015, 10:33
Expert's post
00:00

Question Stats:

91% (00:20) correct 8% (00:00) wrong based on 12 sessions
$$x^2 - 1 = y$$
$$x = 3$$

Quantity A: $$y^2$$
Quantity B: 80

• Quantity A is greater.
• Quantity B is greater.
• Both Quantities are Equal
• Cannot be determined
[Reveal] Spoiler: OA

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Re: GRE Math Challenge #73- x^2 - 1 = y and x = 3 [#permalink]  08 Aug 2017, 07:13
Expert's post
sandy wrote:
$$x^2 - 1 = y$$
$$x = 3$$

Quantity A: y²
Quantity B: 80

• Quantity A is greater.
• Quantity B is greater.
• Both Quantities are Equal
• Cannot be determined

Given:
x² - 1 = y
x = 3

So, in the top equation, REPLACE x with 3 to get: 3² - 1 = y
Evaluate to get: 9 - 1 = y
So, y = 8

We must compare...
Quantity A: y²
Quantity B: 80

Replace y with 8 to get:
Quantity A: 8²
Quantity B: 80

Evaluate to get:
Quantity A: 64
Quantity B: 80

[Reveal] Spoiler:
B

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Re: GRE Math Challenge #73- x^2 - 1 = y and x = 3   [#permalink] 08 Aug 2017, 07:13
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