What is the value of 5x^2 +4x-1?
1) x(x+2)=0
2)x=0
Statment 1 gives you 2 roots for x and the problem has an x^2, shouldn't that be the correct answer if you simplify the question as
x(5x+4)=1?
THanks,
GMAT Forum
4 postsPage 1 of 1
- Mariela
- GMATPaduan
DS Response
Rephrase the question to: What is X?
(1) x(x+2)= 0
Not sufficient: x could be 0, or x could be -2
2) x=0
Sufficient - gives a value for x
(1) x(x+2)= 0
Not sufficient: x could be 0, or x could be -2
2) x=0
Sufficient - gives a value for x
- Jeff
OG 11th ed Data sufficiency # 97
Mariela -
The question statement asks what the value of 5x^2+4x-1 is...it does not tell you that 5x^2+4x-1=0, so you can't simplify it to x(5x+4)=1. To answer the question, you need to know the value of x, or the value of the factors (5x-1)(x+1), or know that one of those factors =0 (which would mean that 5x^2+4x-1=0).
Fact (2) gives us the value of x directly (x=0) so we then know that 5x^2+4x-1=-1 and (2) is sufficient by itself.
Fact (1) tells us that x=0 or x=-2. If x=0 then 5x^2+4x-1=-1. If x=-2 then 5x^2+4x-1= 11 so (1) is not sufficient by itself and the answer is B
Best,
Jeff
The question statement asks what the value of 5x^2+4x-1 is...it does not tell you that 5x^2+4x-1=0, so you can't simplify it to x(5x+4)=1. To answer the question, you need to know the value of x, or the value of the factors (5x-1)(x+1), or know that one of those factors =0 (which would mean that 5x^2+4x-1=0).
Fact (2) gives us the value of x directly (x=0) so we then know that 5x^2+4x-1=-1 and (2) is sufficient by itself.
Fact (1) tells us that x=0 or x=-2. If x=0 then 5x^2+4x-1=-1. If x=-2 then 5x^2+4x-1= 11 so (1) is not sufficient by itself and the answer is B
Best,
Jeff
- dbernst
- ManhattanGMAT Staff
- Posts: 300
- Joined: Mon May 09, 2005 9:03 am
OG 11th ed Data sufficiency # 97
Jeff, thanks for the explanation. I was wondering where you have been!
Mariela, as I stated on your other submission, it is extremely important on Data Sufficiency to practice carefully rephrasing the original question. However, be sure to review your math fundamentals (especially with algebra) so that you don't accidentally go "too far" with your rephrase (i.e. break rules of mathematics). As Jeff noted, in this case you set the original equation equal to zero, but the problem never told you that this equation was equal to zero. On the GMAT, be sure to only utilize the information given. Don't assume anything!!!
-dan
Mariela, as I stated on your other submission, it is extremely important on Data Sufficiency to practice carefully rephrasing the original question. However, be sure to review your math fundamentals (especially with algebra) so that you don't accidentally go "too far" with your rephrase (i.e. break rules of mathematics). As Jeff noted, in this case you set the original equation equal to zero, but the problem never told you that this equation was equal to zero. On the GMAT, be sure to only utilize the information given. Don't assume anything!!!
-dan
4 posts Page 1 of 1