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What is the value of xy - yz?

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BTGModeratorVI: Legendary Member; Posts: 1223; Joined: Sat Feb 15, 2020 2:23 pmFollowed by: 1 member

by BTGModeratorVI » Wed Oct 07, 2020 7:12 am

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What is the value of xy - yz?

(1) y = 2
(2) x - z = 5

Answer: C
Source: Official guide

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Source: Beat The GMAT — Data Sufficiency | Wed Oct 07, 2020 7:12 am

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

Re: What is the value of xy - yz?

by Brent@GMATPrepNow » Sat Oct 10, 2020 7:18 am

BTGModeratorVI wrote: ↑
Wed Oct 07, 2020 7:12 am
What is the value of xy - yz?

(1) y = 2
(2) x - z = 5

Answer: C
Source: Official guide

Important: Notice that we can take xy - yz and factor out the y to get the following equivalent expression: y(x - z)

Target question: What is the value of y(x - z)?

Statement 1: y = 2
Our goal is to determine the value of y(x - z)
We now know the value of y, but we don't know the value of (x - z)
Statement 1 is NOT SUFFICIENT

Statement 2: x - z = 5
Our goal is to determine the value of y(x - z)
We now know the value of (x - z), but we don't know the value of y
Statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that y = 2
Statement 2 tells us that x - z = 5
So, y(x - z) = 2(5) = 10
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer: C

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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deloitte247: Legendary Member; Posts: 2214; Joined: Fri Mar 02, 2018 2:22 pmFollowed by: 5 members

Re: What is the value of xy - yz?

by deloitte247 » Sat Oct 17, 2020 7:35 pm

To find the target question (i.e the value of xy - yz), we have to evaluate both statements' conditions.

Statement 1: y=2
There is no given value for x and z; this implies that we cannot estimate the value for xy-yz. So, therefore, statement 1 is NOT SUFFICIENT.

Statement 2: x-z=5
There is no given value for y; this implies that we cannot estimate the value for xy-yz. So, therefore, statement 2 is NOT SUFFICIENT.

Combining both statements:
From statement 1, y=2
From statement 2, x-z=5
xy - yz
y (x-z) = 2(5) = 10
Since this combination of both statements answers the target question, then it is SUFFICIENT.

The answer is, therefore, option C.

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