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# If (3x+3)^2 = 900, which of the following could be the value of x -1?

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Director
Joined: 22 Feb 2018
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If (3x+3)^2 = 900, which of the following could be the value of x -1?  [#permalink]

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11 Feb 2020, 00:28
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If (3x+3)^2 = 900, which of the following could be the value of x -1?

A)-12
B) -11
C) -8
D) 9
E) 11
GMAT Tutor
Joined: 24 Jun 2008
Posts: 2012
Re: If (3x+3)^2 = 900, which of the following could be the value of x -1?  [#permalink]

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11 Feb 2020, 06:50
if a^2 = 900, then a is either 30 or -30. So here we have two possibilities:

3x + 3 = 30
3x = 27
x = 9
x-1 = 8

but that's not an answer choice. So the answer must come from this equation

3x + 3 = -30
3x = -33
x = -11
x-1 = -12
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Director
Joined: 12 Dec 2015
Posts: 516
Re: If (3x+3)^2 = 900, which of the following could be the value of x -1?  [#permalink]

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11 Feb 2020, 08:59
If (3x+3)^2 = 900, which of the following could be the value of x -1?

A)-12 --> correct: (3x+3)^2 = 900 => 9*(x+1)^2=900 => (x+1)*2 = 100 => x+1 = +10 or -10 => x-1= +8 or -12
B) -11
C) -8
D) 9
E) 11
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Re: If (3x+3)^2 = 900, which of the following could be the value of x -1?  [#permalink]

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17 Feb 2020, 03:19
Raxit85 wrote:
If (3x+3)^2 = 900, which of the following could be the value of x -1?

A)-12
B) -11
C) -8
D) 9
E) 11

Taking the square root of both sides, we have:

3x + 3 = 30

3x = 27

x = 9

Or

3x + 3 = -30

3x = -33

x = -11

Thus, x - 1 could be either 8 or -12.

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Re: If (3x+3)^2 = 900, which of the following could be the value of x -1?  [#permalink]

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17 Feb 2020, 15:47

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Re: If (3x+3)^2 = 900, which of the following could be the value of x -1?   [#permalink] 17 Feb 2020, 15:47
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