inputs needed on these two questions

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rohittk: Junior | Next Rank: 30 Posts; Posts: 27; Joined: Thu Jun 04, 2009 11:05 am; Thanked: 2 times; GMAT Score:670

by rohittk » Thu Oct 08, 2009 1:50 am

(a) In the xy co-ordinate plane, line l and line k intersect at the point(4,3). Is the product of their slopes negative?
(1) Product of the x intercept of line l and k is positive.
(2) Product of the y intercept of the lines l and k is negative.

(b) If k is a positive integer, is k a square of an integer?
(1) K is divisible by 4.
(2) k is divisible by exactly 4 different prime numbers.

I will appreciate answers with explanations to the above two questions. Thank You.

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Source: Beat The GMAT — Data Sufficiency | Thu Oct 08, 2009 1:50 am

ershovici: Senior | Next Rank: 100 Posts; Posts: 91; Joined: Tue Aug 25, 2009 7:50 am; Location: Washington DC; Thanked: 2 times; GMAT Score:600

by ershovici » Thu Oct 08, 2009 3:39 am

First one.
We need two lines, so we should make a scetch. Then try to drow this lines.
St. 1 is insufficient because their x intercept could be both positive or both negative.
St. 2 is insufficient because, because two lines could have different x intercepts and tehir slopes cold vary.
Both St. together are sufficient, and we have only one posibility - both x intercepts are positive and y intercepts - one positive and one negative.

The answer is C

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mehravikas: Legendary Member; Posts: 1161; Joined: Mon May 12, 2008 2:52 amFollowed by: 1 member; Location: Sydney; Thanked: 23 times

by mehravikas » Thu Oct 08, 2009 8:42 pm

I think statement 'B' is sufficient for the first question.

ershovici wrote:First one.
We need two lines, so we should make a scetch. Then try to drow this lines.
St. 1 is insufficient because their x intercept could be both positive or both negative.
St. 2 is insufficient because, because two lines could have different x intercepts and tehir slopes cold vary.
Both St. together are sufficient, and we have only one posibility - both x intercepts are positive and y intercepts - one positive and one negative.

The answer is C

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ershovici: Senior | Next Rank: 100 Posts; Posts: 91; Joined: Tue Aug 25, 2009 7:50 am; Location: Washington DC; Thanked: 2 times; GMAT Score:600

by ershovici » Fri Oct 09, 2009 3:55 am

I am still sure that the answer is C
Here is my reasoning:
Just imagine a line that intersepts Y = 1 and a line which intersepts Y at -1, if both line s also intersept a point 4:3 the product of their slopes would be positive. but if one of the lines intersept Y axis at a point greater that Y =3 and they still have both X intersepts positive, so they would have oposite slopes and their product would be positive.

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Katrusya: Senior | Next Rank: 100 Posts; Posts: 49; Joined: Tue May 19, 2009 10:48 am; Location: Chicago; Thanked: 1 times; GMAT Score:680

by Katrusya » Fri Oct 09, 2009 11:31 am

Rohittk,
I think in (a) the answer is C because we need to know about both Y and X interseptions in order to figure out the slopes of both lines.

(b)
1. K could be 12,16,20 - some of them are not square - not sufficient
2. Let's take for example that K is divisible by 2,3,5,and 7. Product of these gives as 210 (not square)
OR
3,5,7,11 that give us 1155 which is not square also. I think B is the answer here

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mehravikas: Legendary Member; Posts: 1161; Joined: Mon May 12, 2008 2:52 amFollowed by: 1 member; Location: Sydney; Thanked: 23 times

by mehravikas » Fri Oct 09, 2009 1:58 pm

My mistake - For the first question answer should be 'C' we need both the statements to find out the sign of the slopes.

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crackgmat007: Legendary Member; Posts: 882; Joined: Fri Feb 20, 2009 2:57 pmFollowed by: 1 member; Thanked: 15 times; GMAT Score:690

by crackgmat007 » Fri Oct 09, 2009 5:49 pm

Katrusya wrote:Rohittk,
I think in (a) the answer is C because we need to know about both Y and X interseptions in order to figure out the slopes of both lines.

(b)
1. K could be 12,16,20 - some of them are not square - not sufficient
2. Let's take for example that K is divisible by 2,3,5,and 7. Product of these gives as 210 (not square)
OR
3,5,7,11 that give us 1155 which is not square also. I think B is the answer here

I think answer is E for second question.

A - K could be 16 or 24 - not sufficient
B - Lets say the number is 3*5*7*11*3*5*7*11. This number is a perfect sqare - not sufficient

A&B K can be 3*5*7*11*2*2 (not a perfect square) or 3*5*7*11*3*5*7*11*2*2 (a perfect square) Hence E

Both 1 & 2

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imanemekouar: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Wed Dec 16, 2009 6:39 am

by imanemekouar » Wed Jan 06, 2010 6:35 am

can you lease explain the problem. I really did not get it.

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