Algebra question

Expert replies

ornelaspedro: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Wed Feb 18, 2009 9:15 pm

by ornelaspedro » Wed Apr 29, 2009 7:02 pm

Can anybody tell me how to solve this;

If xy + z = x(y + z), which of the following must be true?

a) x = 0 and z = 0
b) x = 1 and y = 1
c) y = 1 and z = 0
d) x = 1 and y =0
e) x = 1 and z = 0

The answer is E, I solved for x and got one, however, I'm uncertain on how the answer is z = 0 and not y = 0

Like this post

Source: Beat The GMAT — Problem Solving | Wed Apr 29, 2009 7:02 pm

keizer Soze: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Mon Apr 27, 2009 6:15 pm; Thanked: 1 times; GMAT Score:650

by keizer Soze » Wed Apr 29, 2009 7:26 pm

The last equation is z=zx

so here x=1 and z must be 0

y could be 0 also, but it musn´t be 0, it could be any other number. I think that there is the key.

Like this post

lilu: Master | Next Rank: 500 Posts; Posts: 148; Joined: Wed Dec 10, 2008 5:13 pm; Location: SF, CA; Thanked: 12 times

by lilu » Wed Apr 29, 2009 7:47 pm

xy+z=xy+xz-->z=xz-->z-xz=0--->z(1-x)=0----->z=0, x=1------>E

The more you look, the more you see.

Like this post

marcusking: Master | Next Rank: 500 Posts; Posts: 106; Joined: Wed Feb 04, 2009 6:09 am; Location: Louisville, KY; Thanked: 8 times

Re: Algebra question

by marcusking » Thu Apr 30, 2009 5:46 am

ornelaspedro wrote:Can anybody tell me how to solve this;

If xy + z = x(y + z), which of the following must be true?

a) x = 0 and z = 0
b) x = 1 and y = 1
c) y = 1 and z = 0
d) x = 1 and y =0
e) x = 1 and z = 0

The answer is E, I solved for x and got one, however, I'm uncertain on how the answer is z = 0 and not y = 0

So what I don't get is why c wouldn't be a possibility too.

x=-5
y=1
z=0
-5*1 + 0 = -5(1+0)
With c both sides would always be equal to the value of x

I understand E works but doesn't C also?

Like this post

keizer Soze: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Mon Apr 27, 2009 6:15 pm; Thanked: 1 times; GMAT Score:650

by keizer Soze » Thu Apr 30, 2009 8:07 am

C is a posibility, but there Y could be any other number, and the question asked which MUST be true... you can´t be sure that y=1... it could be y=2 or y=3...

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review