Target question: At what point does the line ax + y + b = 0 intersect the y-axis?
This is a great candidate for REPHRASING THE TARGET QUESTION

Take the equation of the line ax + y + b = 0, and rewrite it in SLOPE Y-INTERCEPT FORM
Given: ax + y + b = 0
Subtract ax and b from both sides to get: y = -ax - b
At this point, we can see that the y-intercept is -b (and the slope is -a)
So, to determine the y-intercept, we need only determine the value of b
REPHRASED target question: What is the value of b?

Statement 1: b = 5
PERFECT!!
Since we can answer the REPHRASED target question with certainty, statement 1 is SUFFICIENT

Statement 2: a = 3
We cannot use this information to determine the value of b.
Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT

Answer = A
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The answer is A.

(1) b = 5
ax + y + b = 0
y + b =0 (x=0; where the line intersect y axis)
y=-b and b is given hence Sufficient


(2) a = 3
a is the slope
ax + y + b = 0
y=-ax - b
y=-b (x=0; where the line intersect y axis)

No value for y hence Insufficient.

Lets rewrite the equation,ax+y+b=0 or,y=-ax-b

(1) When the line intersect the y axis ,we can write the equation,y=-a*0-b=-b.Since b=5,So y=-5.So the line intersects at (0,-5),Sufficient

(2) When the line intersect the y axis ,we can write the equation,y=-a*0-b=-b.here given a=3,but we don't know the value of b,Insufficient

Correct Answer A

I tend to investigate and make it the most visual possible to understand why the right answer is right and the other way round.

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Posted from my mobile device

This question just gives the formula for the slope of a line as ax instead of mx- just rearrange

y=-ax-b

Statement 1

The b value in y=mx +/- b is the y-intercept

Suff

Statement 2

This value is just the slope

Insuff


Thus

A

At what point does the line ax + y + b = 0 intersect the y-axis?

(1) b = 5

(2) a = 3

At what point does the line ax + y + b = 0 intersect the y-axis?
Means ,
X=0
so the equation becomes y+b=0
therefore y = -b

Hence we only need to know the value of B , to get the answer .

Hence statement A is sufficient .

Hi Bunuel ,
My approach is correct ? . Please confirm .

Regards,

Yes. You could check the solutions above to check it.
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