The answer would be B. Second statement alone is sufficient.ikaplan wrote:If x+xy+y=-1, then what is the value of x+y?
(1) y=-1
(2) x=2
Source: NOVA's GMAT DS Prep Course, p.65
What is OA?
DS: (x+y)
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What is OA?
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rohit_gmat
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trick Q?ikaplan wrote:If x+xy+y=-1, then what is the value of x+y?
(1) y=-1
(2) x=2
Source: NOVA's GMAT DS Prep Course, p.65
stmnt 1) y = -1 ... putting this in our equation gives us :
x + x(-1) + (-1) = -1
x - x -1 = -1
-1 = -1 ==> this doesn't give us any value for x, so we cant find out what x+y equals to
INSUFF
stmnt 2) x = 2 ... putting this in our equation gives us :
2 + 2y + y = -1
3y = -1 -2
3y = -3
y = -1
x =2 & y=-1 ... so x+y = 1
SUFF
Answer B
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Brent@GMATPrepNow
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I'll offer another approach here, since it's always nice to have several options when solving a question.ikaplan wrote:If , then what is the value of x+y?
(1) y=-1
(2) x=2
Source: NOVA's GMAT DS Prep Course, p.65
For me, when I see a given equation like x+xy+y=-1, I consider whether there's a way to rearrange it such that I can gain some information about x and y.
Here, we can rewrite the given equation as x+xy+1+y=0. Then we can factor it in parts (a useful technique when dealing with 4-term algebraic expressions).
When we factor it in parts we get: x(1+y) + 1(1+y)=0
We can now simplify this as (x+1)(1+y)=0
This tells us that x= -1 or y= -1 (or they both equal -1)
Okay, now let's examine the statements:
Statement 1: y= -1
If y= -1, we can see that x can have any value, which means x+y can have any value.
As such, statement 1 is not sufficient.
Statement 2: x = 2
If x = 2, then it must be true that y=-1 (since we already concluded that x= -1 or y= -1 (or they both equal -1))
So we know that x=2 and we know that y must equal -1.
As such, we can find the value of x+y (it equals 1), so statement 2 is sufficient, and the answer is B
Of course, rohit_gmat's solution is quicker, but I thought I'd post another approach nonetheless.
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
