Data Sufficiency

In the xy-plane line a and b have same slope .if the y- of the line a is -1.what is the y- intercept of line b.

1)the x-intercept of line a is -1.

2)line b passes through the point (10,20)

Md.Nazrul Islam wrote:In the xy-plane line a and b have same slope.if the y- of the line a is -1.what is the y- intercept of line b.

1)the x-intercept of line a is -1.

2)line b passes through the point (10,20)

Line a: y=mx + s= mx-1
Line b: y=mx + w ; w=?

for line a:

at x=0; y=s=-1

1) from this we can have ;
s/m=1
=> m=-1
we cant have w

INSUFFICIENT

2) 20=10m+w

INSUFFICIENT

1) +2)

WE HAVE m=-1
hence we can have w

SUFFICIENT

Hence C

Coordinate Geometry is generally about distance or line equation with slope. here we have a line equation problem.

if we know the x intercept of line a we still don't knwo the orientation of line b at all, just that it has the same slope ( in this case a negative slope as it goes from (-1,0) to (0, -1). Insufficient, leave BCE

You need two points to find the slope of a line and this one point plus the incomplete point of the statement above is not enough to find slope or intercept.

If you put them together you have both a slope (from statement 1) and a point on the line to give you the placement of the line. YOu can use both to find the y intercept.