We need to find whether info is sufficient to find value of y-x2-x.

We cant simplify the question stem further, so lets start with st1:
(1) y = -3x --> two vars 1 eq--> cant solve
(2) y = -4(x + 1) --> two vars 1 eq--> cant solve

1+2 together is solvable.
y=-3x and also y=-4x-4

so -3x=-4x-4
x=-4, y=12
we dont actually need to solve but for illustration i did. Knowing that we can solve them to get unique values of x and y is enough.

So 1 and 2 taken together are sufficient

Best Regards,
Mansoor

PS: Please Consider Kudos if you find it helpful

What is the value of \(y-x^2-x\)?

(1) y = -3x --> the question becomes: what is the value of \(-3x-x^2-x\). We need the value of x to answer this question. Not sufficient.

(2) y = -4(x + 1) --> the question becomes: what is the value of \(-4(x + 1)-x^2-x\). We need the value of x to answer this question. Not sufficient.

(1)+(2) We have two distinct linear equations: \(y = -3x\) and \(y = -4(x + 1)\), thus we can solve for both variables and get the value of \(y-x^2-x\). Sufficient.

Answer: C.

Hope it's clear.
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The explanation about linear equation is not clear

Hi All,

This DS question can be solved with a combination of TESTing VALUES and Algebra skills.

We're asked for the value of Y - X^2 - X.

Fact 1: Y = -3X

IF....
X = 0
Y = 0
The answer to the question is 0 - 0^2 - 0 = 0

IF...
X = 1
Y = -3
The answer to the question is -3 - 1^2 - 1 = -5
Fact 1 is INSUFFICIENT

Fact 2: Y = -4(X+1)

IF...
X = 0
Y = -4
The answer to the question is -4 - 0^2 - 0 = -4

IF...
X = 1
Y = -8
The answer to the question is -8 - 1^2 - 1 = -10
Fact 2 is INSUFFICIENT

Combined, we know...
Y = -3X
Y = -4(X+1)

Looking at this, you should recognize a "system" of equations - we can set the equations equal to one another...

-3X = -4X - 4
X = -4

With one fixed value for X, we can solve for Y:

Y = -3(-4) = 12

Thus, X = -4 and Y = 12, so we CAN answer the question.
Combined, SUFFICIENT

Final Answer:

GMAT assassins aren't born, they're made,
Rich
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