CMAT Club Test Question - m25

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CMAT Club Test Question - m25 [#permalink]

30 Sep 2010, 04:10

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41% (00:56) wrong

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Hello,
Am new here. I just took the m25 GMAT CLub Test and I don't get the solution of a question. (Q19)

If equation |\frac{x}{2}| + |\frac{y}{2}| = 5 encloses a certain region on the coordinate plane, what is the area of this region?
20
50
100
200
400

OA: 200

ME: well, since |x| + |y| = 10 ; X can range from (-10) to (10) (when Y is 0) and the same for Y
So the length of the side of the square should be 20.
My Answer : 400

I think I am making a silly mistake some where but I just can't figure it out.

Thanks

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Re: CMAT Club Test Question - m25 [#permalink]

30 Sep 2010, 04:22

Barkatis wrote:

Hi and welcome to the Gmat Club. Below is the solution for your problem. Hope it's clear.

|\frac{x}{2}| + |\frac{y}{2}| = 5

You will have 4 case:

x<0 and y<0 --> -\frac{x}{2}-\frac{y}{2}=5 --> y=-10-x;

x<0 and y\geq{0} --> -\frac{x}{2}+\frac{y}{2}=5 --> y=10+x;

x\geq{0} and y<0 --> \frac{x}{2}-\frac{y}{2}=5 --> y=x-10;

x\geq{0} and y\geq{0} --> \frac{x}{2}+\frac{y}{2}=5 --> y=10-x;

So we have equations of 4 lines. If you draw these four lines you'll see that the figure which is bounded by them is square which is turned by 90 degrees and has a center at the origin. This square will have a diagonal equal to 20, so the Area_{square}=\frac{d^2}{2}=\frac{20*20}{2}=200.

Or the Side= \sqrt{200} --> area=side^2=200.

Answer: D.

Check similar problem at: graphs-modulus-help-86549.html?hilit=horizontal#p649401 it might help to get this one better.

Hope it helps.
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Re: CMAT Club Test Question - m25 [#permalink]

30 Sep 2010, 04:44

Thanks, the 20 was actually for the diagonals not the sides !

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Re: CMAT Club Test Question - m25 [#permalink]

30 Sep 2010, 17:41

|X/2| + |Y/2| = 5
so when x = 0, y= |10|
when y=0 , x=|10|

so the sides of the enclosed area touches (0,10),(10,0),(0,-10) and (-10,0).
so its a square having the diagonal =20unit
So the area of the region = (20/1.414)^2 = 200

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Re: CMAT Club Test Question - m25 [#permalink]

12 Oct 2010, 08:45

i first didnt consider the mod value got the answer as 50.later i realised my mistake

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Re: GMAT club test m25 #19 [#permalink]

04 Nov 2010, 16:56

I think it is sometimes easy to solve a question by plotting it in graph. I to initially got the answer as 400 but plotting the same on the graph gave me the correct vertices and eventually I was able to solve the problem.

Thank you guyz.....
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Re: CMAT Club Test Question - m25 [#permalink]

16 Nov 2010, 09:45

|x|+||y|=10

put x=0

you get |y|=10 .....y=+-10

when you y=0

you get |x| = 10 ..... x=+-10

plot this on the co-ordinate plane.

you will get a rhombus
area of rhombus = 1/2 (d1 x d2)= 20X20/2= 200

Re: CMAT Club Test Question - m25 [#permalink] 16 Nov 2010, 09:45

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