The line 3x + 4y = 8 passes through all of the quadrants in

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The line 3x + 4y = 8 passes through all of the quadrants in [#permalink]

09 Oct 2012, 12:28

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The line 3x + 4y = 8 passes through all of the quadrants in the coordinate plane except:

A. I
B. II
C. III
D. IV
E. II and IV.

[Reveal] Spoiler: OA

Last edited by Bunuel on 09 Oct 2012, 13:56, edited 3 times in total.

Edited the question and added the OA.

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Re: The line 3x + 4y = 8 passes through all of the quadrants in [#permalink]

09 Oct 2012, 14:21

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venmic wrote:

The line 3x + 4y = 8 passes through all of the quadrants in the coordinate plane except:

A. I
B. II
C. III
D. IV
E. II and IV.

Notice that if both x and y are negative, then both 3x and 4y will be negative. The sum of two negative values (3x and 4y) cannot give positive result (8). Thereore the line does not pass through the third quadrant, where both x and y are negative.

Answer: C.

Check the diagram below:

Attachment:

graph.png [ 6.97 KiB | Viewed 681 times ]

Hope it's clear.
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Re: The line 3x + 4y = 8 passes through all of the quadrants in [#permalink]

09 Oct 2012, 16:14

venmic wrote:

The line 3x + 4y = 8 passes through all of the quadrants in the coordinate plane except:

A. I
B. II
C. III
D. IV
E. II and IV.

This is a line which doesn't pass through the origin. We know because there is a free term (which doesn't contain neither x, nor y).
In this case, we can use the intercept form of the line equation: divide through the equation by the free term 8. We get:
\frac{3x}{8}+\frac{4y}{8}=1 or \frac{x}{8/3}+\frac{y}{8/2}=1, and finally \frac{x}{2\frac{2}{3}}+\frac{y}{2}=1.

Now, we can easily see that the x intercept is 2\frac{2}{3} and the y intercept is 2.
So, our line passes through the points (2\frac{2}{3},0) and (0,2). Sketch the line through these two points.
It is a decreasing line which doesn't pass through the third quadrant.

Answer C.
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Re: The line 3x + 4y = 8 passes through all of the quadrants in [#permalink] 09 Oct 2012, 16:14

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The line 3x + 4y = 8 passes through all of the quadrants in

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The line 3x + 4y = 8 passes through all of the quadrants in

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