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more ds from gmat prep

by xcise_science » Sat Dec 01, 2007 4:42 pm
q18,
stmt 1: 6=x+y
stmt 2: 130=.23x + .21y
Why is B the answer? I thought you can't solve if you have 2 variables and 1 equation

Image

q33

Image

q6
I just guessed that C was the answer to this, I didn't really understand stmt2

Image
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by syv11 » Sat Dec 01, 2007 4:50 pm
q18

23x+21y=130

you know that x and y have to be integers; the only set of numbers that solves for 130 total price is x=2 and y=4

Therefore B

If you did not know that x and y have to be integers, you were right
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by syv11 » Sat Dec 01, 2007 4:59 pm
q33

1993 1000
1994 1000*(1+x/100)
1995 1000*(1+x/100)*(1+y/100)=1000*(1+x/100+y/100+xy/10000)

(1) not enough
(2) enough so solution is 1000*(1+9.2/100)
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by syv11 » Sat Dec 01, 2007 4:59 pm
q 33 ==> B
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by syv11 » Sat Dec 01, 2007 5:06 pm
q6

(1) alone is not sufficient, does not tell us anything about (u,v)
(2) try to insert number in 1:

could be u=5, r=-4 and v=5, s=-4 i.e not equidistant or
u=2, r=-1 and v=-1, r=2 i.e. equidistant

If you combine that with statement (1) you will see that all pairs are equidistant; just try a couple more numbers
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by xcise_science » Sat Dec 01, 2007 5:30 pm
re: q18
oh, so when I have an unequal # of variables & equations I can guess/plug in as long as I know the variables are integers?

Thats good to know.

thanks
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by xcise_science » Sat Dec 01, 2007 5:36 pm
Thank.
Can you explain this part:
how did you go from here:
1995 1000*(1+x/100)*(1+y/100)=1000*(1+x/100+y/100+xy/10000)
TO:
(2) enough so solution is 1000*(1+9.2/100)
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by syv11 » Sat Dec 01, 2007 5:44 pm
1995 1000*(1+x/100)*(1+y/100)=1000*(1+[b]x/100+y/100+xy/10000[/b]) ==> the number in the parenthesis is just multiplying out (1+x/100)*(1+y/100)

Then, you have given x+y+xy/100=9.2 ==> divide by 100 and you get

[b]x/100+y/100+xy/1000=0.092[/b] ==> replace this in the first line and you get

1000*(1+0.092)

Is this clear?
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by xcise_science » Sat Dec 01, 2007 9:01 pm
barely.

let me ask you, if you saw this question on the test, how long will it take you
to work out this explanation? Also, did you see from stmt 2 that it might be sufficient or was it while doing the calculations, that you determined B was sufficient?


Thanks
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