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What is the value of $xy - yz?$

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Gmat_mission: Legendary Member; Posts: 1622; Joined: Thu Mar 01, 2018 7:22 amFollowed by: 2 members

by Gmat_mission » Fri Nov 20, 2020 1:48 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 | Fri Nov 20, 2020 1:48 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 » Thu Nov 26, 2020 1:46 pm

Gmat_mission wrote: ↑
Fri Nov 20, 2020 1:48 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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