If x y and z are positive is xz = 7xy?

This topic has expert replies
Source: — Data Sufficiency |

User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Sat Apr 28, 2018 2:22 am

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

M7MBA wrote:If x y and z are positive is xz = 7xy?

(1) z/y = 7
(2) x/y = 1
Since x is positive, we can divide both sides of the question stem by x:
xz/x = 7xy/x
z =7y.
Questions stem, rephrased:
Does z = 7y?

Statement 1:
z/y = 7
z = 7y.
Thus, the answer to the question stem is YES.

Statement 2:
No information about z.
INSUFFICIENT.

The correct answer is A.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

Legendary Member
Posts: 2898
Joined: Thu Sep 07, 2017 2:49 pm
Thanked: 6 times
Followed by:5 members

by Vincen » Sat Apr 28, 2018 2:25 am

Timer

00:00

Your Answer

A

B

C

D

E

Global Stats

Hello gmat_mission.

(1) z/y = 7

This statement implies that z=7y. Therefore, $$xz=x\left(7y\right)=7xy.$$ Hence, the answer is YES. SUFFICIENT.

(2) x/y = 1

This statement tells us that x=y. Hence $$7xy=7x^2=7y^2.$$ Since we don't know anything about z, we don't know if xz=7xy. NOT SUFFICIENT.

Hence, the correct answer is the option A