Tuesday, January 08, 2008

Data Sufficiency - 34

In the xy-plane, at what two points does the graph of y=(x+a)(x+b) intersect the x-axis?

1). a+b= -1
2). The graph intersects the y-axis at (0,-6)

Answer: C

From Statement (1) -- a+b = -1...no information about a and b ...hence insufficient

From Statement (2) -- If x = 0 the y = -6 thus ab = 6....insufficient

Taking statements (1) and (2) together: (x+a)*(x+b)=0

x^2+(a+b)x+ab=0

Hence x=-3, x=2

Thus the answer C