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655-705 Level|   Algebra|      
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Bunuel
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What is the value of x ? (1) x^2 - 1 = x + 1 (2) x + 3 is a prime 28 Jun 2023, 02:57
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E
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Difficulty:

65% (hard)

Question Stats:

50% (01:13) correct 50% (01:08) wrong based on 136 sessions

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What is the value of x ?

(1) x^2 - 1 = x + 1
(2) x + 3 is a prime number
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Official Answer
E
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Archit3110
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What is the value of x ? (1) x^2 - 1 = x + 1 (2) x + 3 is a prime 29 Jun 2023, 03:08
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#1
x^2 - 1 = x + 1
solve for x we get
2,-1
#2
x + 3 is a prime number
x= 2,-1 , +4
insufficient
from 1 &2
x= 2,-1
option E


Bunuel
What is the value of x ?

(1) x^2 - 1 = x + 1
(2) x + 3 is a prime number
Show more
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HassanZafar
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What is the value of x ? (1) x^2 - 1 = x + 1 (2) x + 3 is a prime 24 Dec 2024, 05:18
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Archit3110
#1
x^2 - 1 = x + 1
solve for x we get
2,-1
#2
x + 3 is a prime number
x= 2,-1 , +4
insufficient
from 1 &2
x= 2,-1
option E


Bunuel
What is the value of x ?

(1) x^2 - 1 = x + 1
(2) x + 3 is a prime number
Show more
Why cant we solve X^2 -1 as (x+1)(x-1). Which will only give the answer of x=2.
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Bunuel
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What is the value of x ? (1) x^2 - 1 = x + 1 (2) x + 3 is a prime 24 Dec 2024, 05:59
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HassanZafar
Archit3110
#1
x^2 - 1 = x + 1
solve for x we get
2,-1
#2
x + 3 is a prime number
x= 2,-1 , +4
insufficient
from 1 &2
x= 2,-1
option E


Bunuel
What is the value of x ?

(1) x^2 - 1 = x + 1
(2) x + 3 is a prime number
Why cant we solve X^2 -1 as (x+1)(x-1). Which will only give the answer of x=2.
Show more


You cannot reduce (x + 1)(x - 1) = x + 1 by x + 1 because x + 1 can be 0 and we cannot divide by 0. By doing so you loose a root, namely x + 1 --> x = -1.

Never reduce equation by a variable (or expression with a variable), if you are not certain that the variable (or expression with the variable) doesn't equal to zero. We cannot divide by zero.


P.S. Pure algebraic questions are no longer a part of the DS syllabus of the GMAT.

DS questions in GMAT Focus encompass various types of word problems, such as:

  • Word Problems
  • Work Problems
  • Distance Problems
  • Mixture Problems
  • Percent and Interest Problems
  • Overlapping Sets Problems
  • Statistics Problems
  • Combination and Probability Problems

While these questions may involve or necessitate knowledge of algebra, arithmetic, inequalities, etc., they will always be presented in the form of word problems. You won’t encounter pure "algebra" questions like, "Is x > y?" or "A positive integer n has two prime factors..."

Check GMAT Syllabus for Focus Edition

You can also visit the Data Sufficiency forum and filter questions by OG 2024-2025, GMAT Prep (Focus), and Data Insights Review 2024-2025 sources to see the types of questions currently tested on the GMAT.

So, you can ignore this question.

Hope it helps.­
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