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moneyman: Master | Next Rank: 500 Posts; Posts: 468; Joined: Sat Mar 03, 2007 10:17 pm; Thanked: 5 times

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by moneyman » Sun Jan 20, 2008 3:36 am

The y intercept of line l is 4. If the slope of l is negative, which of the foll could be the x intercept of l?

(1) -1
(2) 0
(3) 6

Thanks

Maxx

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Source: Beat The GMAT — Problem Solving | Sun Jan 20, 2008 3:36 am

sankruth: Master | Next Rank: 500 Posts; Posts: 195; Joined: Sun Oct 21, 2007 4:33 am; Thanked: 10 times

by sankruth » Sun Jan 20, 2008 4:27 am

(3) 6

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moneyman: Master | Next Rank: 500 Posts; Posts: 468; Joined: Sat Mar 03, 2007 10:17 pm; Thanked: 5 times

by moneyman » Sun Jan 20, 2008 9:14 pm

The Test Prep software is generous enough to give the answers of the questions!! So do you mind giving an explanation for your answer??

Maxx

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camitava: Legendary Member; Posts: 645; Joined: Wed Sep 05, 2007 4:37 am; Location: India; Thanked: 34 times; Followed by:5 members

by camitava » Sun Jan 20, 2008 10:15 pm

moneyman, I don't know how Sankruth chose the option - C. May be I am missing something! But to me, as the st line L is having a negative slope and Y-intercept is positive, I will go for A. So, the slope will come negative. Am I doing something wrong? What's the OA?

Correct me If I am wrong

Regards,

Amitava

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

by Stuart@KaplanGMAT » Mon Jan 21, 2008 6:04 am

If the slope is negative, then the line goes from the top left to the bottom right.

Since the y-intercept is positive and the line is going from top left to bottom right, it will cross the x-axis at a positive coordinate.

Choose the only positive answer:

(3) 6

(Was this a roman numeral question?)

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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Bronson: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Thu Dec 27, 2007 3:48 am; Thanked: 1 times

by Bronson » Mon Jan 21, 2008 6:22 am

Stuart Kovinsky wrote:If the slope is negative, then the line goes from the top left to the bottom right.

Can you explain this? What is negative or positive slope?

Thank you

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

by Stuart@KaplanGMAT » Mon Jan 21, 2008 6:41 am

Bronson wrote:Can you explain this? What is negative or positive slope?

Thank you

The slope of a line is how "slanted" it is. Slope is defined as rise/run or (change in y)/(change in x) = (Y2 - Y1)/(X2 - X1). Slope measures how quickly the line changes vertically (the y-value) compared to how quickly it changes horizontally (the x-value).

In the x-y coordinate plane, "up" and "right" are the positive directions. The top right quadrant has all positive coordinates (i.e. (+,+)) and the bottom left quadrant has all negative coordinates (i.e. (-,-)).

A line with a positive slope goes from bottom left to top right, since (change in y)/(change in x) is positive.

For example, if one point on the line were (-2, -4) and another point were (4, 10), the slope would be:

(change in y/change in x) = (-4 - 2)/(-2 - 10) = -6/-12 = 1/2

A line with a negative slope goes from top left to bottom right, since (change in y)/(change in x) is negative.

For example, if one point on the line were (-2, 4) and another point were (3, -6), the slope would be:

(change in y/change in x) = (4 - -6)/(-2 - 3) = +10/-5 = -2

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camitava: Legendary Member; Posts: 645; Joined: Wed Sep 05, 2007 4:37 am; Location: India; Thanked: 34 times; Followed by:5 members