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In the x-y coordinate plane, lines J, K

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In the x-y coordinate plane, lines J, K  [#permalink]

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New post 30 Jul 2018, 08:28
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Question Stats:

43% (03:30) correct 57% (04:41) wrong based on 30 sessions

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Line J: 4x - 7 = 6y
Line K: 6y + 3x = -2
Line L: 2x = 5 - y

In the x-y coordinate plane, lines J, K and L are defined by the above equations.
Point B is the point of intersection of lines J and K. Point C is the point of intersection of lines K and L.
What is the slope of line segment BC?

A) -3/2
B) -2/3
C) -1/2
D) 1/2
E) 2/3

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Re: In the x-y coordinate plane, lines J, K  [#permalink]

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New post 30 Jul 2018, 09:04
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GMATPrepNow wrote:
Line J: 4x - 7 = 6y
Line K: 6y + 3x = -2
Line L: 2x = 5 - y

In the x-y coordinate plane, lines J, K and L are defined by the above equations.
Point B is the point of intersection of lines J and K. Point C is the point of intersection of lines K and L.
What is the slope of line segment BC?

A) -3/2
B) -2/3
C) -1/2
D) 1/2
E) 2/3


Draw the lines approximately in the x-y coordinate with the help of the slopes. Refer to the figure in attachment below.
J : y=\(\frac{2}{3}\)x-\(\frac{7}{6}\)
K : y=\(\frac{-x}{2}\)-\(\frac{1}{3}\)
L : y=-2x+5
Point B is the point of intersection of lines J and K. Point C is the point of intersection of lines K and L.
Hence BC lies on line K, which has a slope of \(\frac{-1}{2}\).
Answer \(\frac{-1}{2}\) (C).
Attachments

Untitled.jpg
Untitled.jpg [ 12.67 KiB | Viewed 373 times ]


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In the x-y coordinate plane, lines J, K  [#permalink]

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New post 30 Jul 2018, 09:25
GMATPrepNow wrote:
Line J: 4x - 7 = 6y
Line K: 6y + 3x = -2
Line L: 2x = 5 - y

In the x-y coordinate plane, lines J, K and L are defined by the above equations.
Point B is the point of intersection of lines J and K. Point C is the point of intersection of lines K and L.
What is the slope of line segment BC?

A) -3/2
B) -2/3
C) -1/2
D) 1/2
E) 2/3


Great question...
Answer is right there staring at you if you understand it

A point, B ,is at intersection of line J and K and another point, C, is at intersection of K and L.. so points B and C are on line K
When you join B and C, it is nothing but a part of line K..
So slope will be same as that of line K..
\(6y+3x=-2........6y=-3x-2......y=-\frac{3x}{6} -\frac{2}{6}\)
Slope is \(-\frac{3}{6}=\frac{-1}{2}\)

C


Also if you do not get this, other way is..
Take lines J and K
Line J: 4x - 7 = 6y
Line K: 6y + 3x = -2
Two equation two variables, so you will get value of X and y of B
Similarly of C from line K and L..
Slope will be \(\frac{y_B-y_C}{x_B-x_C}\)
You will get answer as -1/2

C
Attachments

PicsArt_07-30-10.08.00.jpg
PicsArt_07-30-10.08.00.jpg [ 42.81 KiB | Viewed 346 times ]


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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


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Re: In the x-y coordinate plane, lines J, K  [#permalink]

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New post 01 Aug 2018, 17:01
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GMATPrepNow wrote:
Line J: 4x - 7 = 6y
Line K: 6y + 3x = -2
Line L: 2x = 5 - y

In the x-y coordinate plane, lines J, K and L are defined by the above equations.
Point B is the point of intersection of lines J and K. Point C is the point of intersection of lines K and L.
What is the slope of line segment BC?

A) -3/2
B) -2/3
C) -1/2
D) 1/2
E) 2/3


Key Concepts: point B lies on line K, and point C lies on line K
Since both points lie on line K, the slope between points B and C will be the same as the slope of line K.


To find the slope of line K, let's take the equation of line K (6y + 3x = -2), and rewrite it in slope y-intercept form (y = mx + b)
Take: 6y + 3x = -2
Subtract 3x from both sides to get: 6y = -3x - 2
Divide both sides by 6 to get: y = (-3/6)x - 2/6
Simplify to get: y = (-1/2)x - 1/3

So, line K has a slope of -1/2 and a y-intercept of -1/3

Answer: C

Cheers,
Brent
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Re: In the x-y coordinate plane, lines J, K &nbs [#permalink] 01 Aug 2018, 17:01
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