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# Really did'nt understand how they approached this

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Director
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Really did'nt understand how they approached this [#permalink]

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31 Oct 2009, 14:02
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31 Oct 2009, 15:09
I'd go with C.

to find the length of QR, we have to know both the y coordinates of Q and R.
similarly, to find length of PR, we have to know both the x coordinates of P and R.

Thus, each statement by itself is insufficient to determine the lengths and hence the ratio.

alternately, the ratio of the lengths can be given by tan(x). where 'x' denotes the slope of the line PQ. In order to find the slope, it is necessary to know both the x and y coordinates of 2 points on the line.

Thus again we can see that each statement by itself would be insufficient but together they would be sufficient.

In this case, length of QR = 4 - (-1) = 5
length of PR = 3 - (-2) = 5

therefore ratio is 1.

whats the OA?
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31 Oct 2009, 15:14
I don't know how OG approached this, but I think in the following way:

the question is "Is QR=PR?"

Given that QR and PR are both parallel to one of axes, their lenths is

for vertical Yh-Yl, or d-b in our case, and
for horizontal Xh-Xl, or c-a.

Refrased question is "Is d-b=c-a?"

Each statement gives coordinate only for one point, each statement alone is NOT SUFFICIENT, but together SUFFICIENT.

KUDOS if you find it helpful
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KUDOS if you find it helpful

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31 Oct 2009, 16:26
tejal777 wrote:

The Q boield down to is PR = QR? --> PR to be = QR --> Angle P = Angle Q. We know that Angle R is a Right angle. --> P+Q = 90. But d/n know their ratio.--> So, we need the co-ordinates of both the points P and Q to measure the length of PR /QR. No info is given about the Triangle PQR (i.e. is it a 30-60-90 triangle). But I understand that If we extend PR, QR is extended proportionately (right triangle theorem).

I would go with C, as neither of the statements is enough to have the slope of the traingle PQR.
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01 Nov 2009, 20:55
OA:
[Reveal] Spoiler:
C

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Director
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02 Nov 2009, 06:09
Could somebody show the workings?
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02 Nov 2009, 06:15
hey,
which part of the solutions above did you have a difficulty in following?
i'll be glad to explain it in a little more detail if you let me know.
cheers!
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02 Nov 2009, 06:31
1
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Consider point $$R$$ as $$R(e, f)$$

Statement 1) $$C=3$$
From this statement you can draw a conclusion that $$e=3$$ as QR is parallel to Y-axis. But we do not know the value of $$f$$. So Insufficient.

Statement 2) $$B=-1$$
From this statement you can draw a conclusion that $$f=-1$$ as PR is parallel to X-axis. But we do not know the value of $$e$$. So Insufficient.

Together, we know that $$e=3 & f=-1$$. So $$R(e,f) = R(3, -1)$$

Now you can find out the distance between P & R, and R & Q:
Dist between P & R = $$\sqrt{(-2-3)^2+(-1-(-1))^2}=5$$
Dist between Q & R = $$\sqrt{(3-3)^2+(4-(-1))^2}=5$$

So Statement 1 and 2 together are sufficient.
Remember, you don't need to calculate the distances to answer the questions. You just need to know if the distances can be calculated using Statement 1 and 2.

Questions? Shoot...
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02 Nov 2009, 06:39
choice C is correct because when data from both statements is provided (that is the coordinates of both the points) it can be possible to determine the lengths of both the lines.

since it is given that QR is parallel to the y-axis and PR is parallel to x-axis, we can find the coordinates of point R.

the x coordinate for R will be the same as that of Q (which is point c)
and the y coordinate will be the same as that of P (which is point b)

therefore coordinates of R will be (c,b)

now in order to calculate the length of QR, we need the y coordinates of both Q and R.. that is points d and b.
(the x coordinates are not necessary since we know that the line is parallel to the y axis.)

similarly, to calculate the length of PR, we need the x coordinates of both P and R.. that is points a and c.
(the y coordinates are not necessary because we know that the line is parallel to x axis.)

thus if we know the numerical value of the points represented by a,b,c and d, we can find the lengths of both the lines (QR and PR).

now, if we know the lengths of both the lines, we can easily find the ratio and see whether or not it will be equal to 1.

if there is any particular statement in my explanation where you loose the flow or cannot understand, just let me know!

hope this helps!

cheers!
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Click below to check out some great tips and tricks to help you deal with problems on Remainders!
http://gmatclub.com/forum/compilation-of-tips-and-tricks-to-deal-with-remainders-86714.html#p651942

1) Translating the English to Math : http://gmatclub.com/forum/word-problems-made-easy-87346.html

Re: Og 11 #78   [#permalink] 02 Nov 2009, 06:39
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