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01 Mar 2015, 13:54
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42%
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Line l in the xy- coordinate system passes through the point ( a,b) where a is not equal to b and ab is not equal 0. What is the slope of line l?
1. The line l passes through point (b,a).
2. a=3, and b= -2
1. The line l passes through point (b,a).
2. a=3, and b= -2
01 Mar 2015, 15:41
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Hi Turkish,
This DS question is based on Graphing rules and can be solved by TESTing VALUES.
We're told that point (A, B) is such that A does NOT equal B and AB does NOT equal 0. These "restrictions" mean that (A, B) is NOT on an axis and cannot be (1,1), (2,2), (-3, -3), etc. We're asked for the slope of a line that passes through point (A,B).
Fact 1: The line also passes through (B,A).
Since the question asks about the slope, it's important to remember that slope = (Change in Y)/(Change in X)
Dealing with idea in the "abstract", we have two co-ordinates: (A,B) and (B,A) so we could plug those variables into the slope 'formula'....
Depending on the "order" of the co-ordinates, you'd have either.....
(B-A)/(A-B)
or
(A-B)/(B-A)
In BOTH situations though, the result is -1
You can TEST VALUES to prove it....
A=1, B=2
(1,2) and (2,1) --> (2-1)/(1-2) = 1/-1 = -1
A=3, B = -1
(3, -1) and (-1,3) --> (-1 - 3)/(3 - -1) = -4/4 = -1
A=-2, B = -3
(-2, -3) and (-3, -2) --> (-3 - -2)/(-2 - -3) = -1/1 = -1
Etc.
The slope is ALWAYS -1
Fact 1 is SUFFICIENT
Fact 2: A=3 and B= -2
This tells us one point on the line (3, -2), but without another point for comparison, we have no idea what the slope of the line is.
Fact 2 is INSUFFICIENT.
Final Answer:
GMAT assassins aren't born, they're made,
Rich
This DS question is based on Graphing rules and can be solved by TESTing VALUES.
We're told that point (A, B) is such that A does NOT equal B and AB does NOT equal 0. These "restrictions" mean that (A, B) is NOT on an axis and cannot be (1,1), (2,2), (-3, -3), etc. We're asked for the slope of a line that passes through point (A,B).
Fact 1: The line also passes through (B,A).
Since the question asks about the slope, it's important to remember that slope = (Change in Y)/(Change in X)
Dealing with idea in the "abstract", we have two co-ordinates: (A,B) and (B,A) so we could plug those variables into the slope 'formula'....
Depending on the "order" of the co-ordinates, you'd have either.....
(B-A)/(A-B)
or
(A-B)/(B-A)
In BOTH situations though, the result is -1
You can TEST VALUES to prove it....
A=1, B=2
(1,2) and (2,1) --> (2-1)/(1-2) = 1/-1 = -1
A=3, B = -1
(3, -1) and (-1,3) --> (-1 - 3)/(3 - -1) = -4/4 = -1
A=-2, B = -3
(-2, -3) and (-3, -2) --> (-3 - -2)/(-2 - -3) = -1/1 = -1
Etc.
The slope is ALWAYS -1
Fact 1 is SUFFICIENT
Fact 2: A=3 and B= -2
This tells us one point on the line (3, -2), but without another point for comparison, we have no idea what the slope of the line is.
Fact 2 is INSUFFICIENT.
Final Answer:
GMAT assassins aren't born, they're made,
Rich
hsbinfy
Joined: 02 Mar 2012
Last visit: 13 Nov 2017
Posts: 196
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05 Jul 2016, 05:33
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slope =y2-y1/x2-x1
so here slope is =b-a/a-b =-1
1) Suff
2)not suff. we need one more point or some other info
A
so here slope is =b-a/a-b =-1
1) Suff
2)not suff. we need one more point or some other info
A
