more ds from gmat prep

xcise_science · Posted: Sat Dec 01, 2007 4:42 pm Post subject: more ds from gmat prep

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

q33

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

syv11 · Posted: Sat Dec 01, 2007 4:50 pm Post subject:

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

syv11 · Posted: Sat Dec 01, 2007 4:59 pm Post subject:

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)

syv11 · Posted: Sat Dec 01, 2007 4:59 pm Post subject:

q 33 ==> B

syv11 · Posted: Sat Dec 01, 2007 5:06 pm Post subject:

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

xcise_science · Posted: Sat Dec 01, 2007 5:30 pm Post subject:

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

xcise_science · Posted: Sat Dec 01, 2007 5:36 pm Post subject:

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)

syv11 · Posted: Sat Dec 01, 2007 5:44 pm Post subject:

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?

xcise_science · Posted: Sat Dec 01, 2007 9:01 pm Post subject:

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