GMATprep PS question

I believe the answer is

1/2 (base)(height)= Area

1/2 (4)(y-intercept) = 12

4(y-intercept) = 24

y-intercept must be -6 because slope of line is positive and crosses the x axis at positive 4. Therefore y intercept must be negative.

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john1234: Senior | Next Rank: 100 Posts; Posts: 47; Joined: Wed May 14, 2008 1:40 pm; Location: United States; Thanked: 2 times; Followed by:1 members

by john1234 » Sat Jul 19, 2008 5:18 pm

believe the answer is

1/2 (base)(height)= Area

1/2 (4)(y-intercept) = 12

4(y-intercept) = 24

y-intercept must be -6 because slope of line is positive and crosses the x axis at positive 4. Therefore y intercept must be negative

How can Y- intercept be negative when the slope is positve and X-intercept is potive(4)?.

Slope Y2-Y1/X2-X1 can only be +ve if Y2 -Y1 is posive and X2-X1 is positve or Y2-Y1 is negative and X2 - X1 is negative.I think Y intercept is + 6.

Even impossible says I M possible

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Mclaughlin: Master | Next Rank: 500 Posts; Posts: 131; Joined: Mon May 05, 2008 10:46 am; Thanked: 1 times

by Mclaughlin » Sat Jul 19, 2008 9:40 pm

What's the OA?

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mlane25269: Master | Next Rank: 500 Posts; Posts: 151; Joined: Fri Jun 13, 2008 7:31 am; Thanked: 1 times

by mlane25269 » Sun Jul 20, 2008 10:20 am

I believe the OA is e) 6 but sorry I didn't get a screenshot of it. I picked 3 which was obviously wrong.

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pepeprepa: Legendary Member; Posts: 661; Joined: Tue Jul 08, 2008 12:58 pm; Location: France; Thanked: 48 times

by pepeprepa » Sun Jul 20, 2008 10:26 am

Just draw it, the answer is -6

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asigheartau: Junior | Next Rank: 30 Posts; Posts: 18; Joined: Sun Jun 22, 2008 11:25 am; Location: NY; Thanked: 1 times

by asigheartau » Sun Jul 20, 2008 12:41 pm

bearing in mind the slope is positive and we know the x intercept to be 4( so positive), the slope has to be in the first quadrant in order to be positive.

Hence, slope is [change in Y/ change in X]. Knowing the x intercept, we know that change in y / 4= a positive number for the slope.
for points (0, y) and (4,0)

Slope: 0-y/4-0 must be positive
-y/4>0 => y needs to have a negative value
A of triangle formed by k is 12 => sides are 4 and 6

X intercept 4,0
Y intercept 0, -6

Last edited by asigheartau on Mon Jul 21, 2008 7:12 pm, edited 1 time in total.

Alin Sigheartau

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pepeprepa: Legendary Member; Posts: 661; Joined: Tue Jul 08, 2008 12:58 pm; Location: France; Thanked: 48 times

by pepeprepa » Sun Jul 20, 2008 1:38 pm

I think the positive slope argument is wrong.

Let's agree about that: A(4;0) B(0;x)
We know the slope has to be positive.
Thanks to the slope formula "Slope=(y-b)/(x-a) for C(x;y) and D(a;b)" let's see what happens when the answer is "6".

"Slope which must be positive"=(0-6)/(4-0)=-6/4 and -6/4<0

Answer is -6.
Tell me if I'm wrong.

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Canman: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Fri Jul 11, 2008 5:00 am; Thanked: 4 times

by Canman » Mon Jul 21, 2008 4:24 am

If y intercept is positive then it violates one of the two restrictions in the question stem:

1) triangle is formed by k and the TWO axes
2) k has a positive slope

I agree with -6 as the answer unless someone can illustrate how +6 can coexist with statements from the stem.

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asigheartau: Junior | Next Rank: 30 Posts; Posts: 18; Joined: Sun Jun 22, 2008 11:25 am; Location: NY; Thanked: 1 times

by asigheartau » Mon Jul 21, 2008 7:05 pm

agreed with you, pepeprepa

The slope has to be positive in order to satisfy the dates of the problem=> y intercept is -6.

Disregards the previous post. Pepeprepa is right

Alin Sigheartau