Some Gmat Prep

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Some Gmat Prep

by holgerrom » Fri May 09, 2008 10:12 am
Hi , i would appreciate if someone could wrote his way of solving the following:


1. If x*y+z = x(y+z), which must be true?
a. x=0 z=0
b. X=1 y=1
c. x=1 z=0

i could find out that x=1 but i cant really get to z=0( the answer is c.). I mean if you solve the equation one gets...z=x*z -->this leads to x =1 but why to Z=0????

2. DS question: If X and Y are positiv integers, what is the value of xy.
a. the greatest common factor is10
b. the least common multiple is 180

can so pls show his calculations here?

3. A certain company has 6 senior and 4 junior officers. If a committee is created out of 3 senior and 1 junior, how many different committees are possible.

here it would be nice if so. could also generally suggest some godd resources to learn probability questions. I thought at first that i had to calculate 6*5*4 for the senior and than take this times 4 as there are four possibilities on the one seat of the junior. But obviously this is wrong.
HMMMM i hate probability...


thxxx
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by II » Fri May 09, 2008 10:38 am
Ok ... so lets start with the first question. Where did you get this question from ? It only has 3 answer choices ... normally there are 5 !

"1. If x*y+z = x(y+z), which must be true?
a. x=0 z=0
b. X=1 y=1
c. x=1 z=0 "

xy + z = x(y+z)
xy + z = xy + xz
z = xz (note: we dont know anything about z ... so we shouldnt divide both sides by z. Instead we should move all the terms onto one side of the equation, as shown below)
z -xz = 0
z(1-x) = 0
which means either z = 0 or 1 - x = 0. If 1 - x = 0, then x = 1.
So x = 1, z = 0.