Data Sufficiency

In the xy-plane, line a and line b have the same slope. If the y-intercept of 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 equations!! I messed up... dont know why~~~ I tried this question again and still come up with C..

Lets get the discussion rolling!

fruti_yum wrote:In the xy-plane, line a and line b have the same slope. If the y-intercept of 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 equations!! I messed up... dont know why~~~ I tried this question again and still come up with C..

Lets get the discussion rolling!

It should be C only as both the statements used together will give a solution. Both statements alone are insufficient.

I think it should be E.

Please correct me if I am wrong.

The lines a and b have the same slope.

Therefore, with the first condition, x intercept of line a is -1.

So, slope of line a is y intercept /x intercept = -1/-1 = 1.

Now, as mentioned in the question, slope of line b should also be 1.

We do not have any information about the y and x intercepts of line b.

So, first option is insufficient.

Now, with the second option, we have no information of the x intercept of line a so we cannot find out its slope. Hence, whatever information is provided about line b is not useful.

So, second option is insufficient.

Combining both options, We still do not have any information about the y and x intercepts of line b.

What do you guys think? Am a lil jittery about this explanation myself.

It should be E
even after having both the condition
we can have
y-20/x-10 = 1 or 20-y/10-x= 1

y-20 ( this is asked) can be any number.....

So E

imo it is C
The data tells us that both lines have same slopes and gives y intercept of a

(1) tells us x intercept of a. So we know two points of line a. So we can plot line a. However line b can be anywhere, although parallel to a!!. So insuff to find out anything about line b
(2) tells us the point through which line b goes. However line b can go through that point to any direction and hence intercept the y axis at any point

But if we combine (1) and (2) we can tell that line b is parallel to line a and that it will always intercept the y axis at a particular point hence combining will be suff to gve us the ans

In the xy-plane, line a and line b have the same slope. If the y-intercept of 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).

C.

From 1 and the question stem we get the slope of line a as -1.
We know a point on line b as (10,20) and let the y-intercept be (0,k).These give the value of the co-ordinate k and hence the Y-intercept of the line can be found as 30