BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Is x = 0 ?

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Master | Next Rank: 500 Posts
Posts: 421
Joined: Sun Apr 17, 2011 4:27 am
Location: India
Thanked: 6 times
Followed by:2 members
GMAT Score:620

Is x = 0 ?

by vinni.k » Tue Jan 08, 2013 6:23 am
Is x = 0 ?

(1) xy = x
(2) x + y = y

answer is B

Why answer cannot be D. Statement (1) gives x = 0 or y = 1. It is giving x = 0. Why should we concerned about y = 1 when we are already getting x = 0 as it is being already asked ?

Thanks & Regards
Vinni
Top
Source: — Data Sufficiency |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Tue Jan 08, 2013 6:32 am
vinni.k wrote:Is x = 0 ?

(1) xy = x
(2) x + y = y
Target question: Is x = 0 ?

Statement 1: xy = x
There are several pairs of values for x and y that meet this condition. Here are two:
Case a: x = 0 and y = 2, in which case x = 0
Case b: x = 3 and y = 1, in which case x = 3
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: x + y = y
Subtract y from both sides to get x = 0
In other words, x must equal 0
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer = B

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Senior | Next Rank: 100 Posts
Posts: 50
Joined: Tue Sep 25, 2012 12:47 am
Thanked: 3 times
Followed by:1 members

by gander123 » Tue Jan 08, 2013 6:37 am
Hey vinni,
Why should we concerned about y = 1 when we are already getting x = 0 as it is being already asked ?
You seem to rule out the possibility that x can be something different than 0. But look closely at statement (1). As you say, y = 1. But then, numerous valous for X satisfy the equation xy = x. Here are some:

(10)*(1) = 10
(9)*(1) = 9
(8)*(1) = 8

and of course (0)*(1)= 0

Hence, you cannot say with absolute certainty that x = 0. Statement (1) is INSUFFICIENT.

Statement (2) just gives you what is asked in the prompt and is thus SUFFICIENT.

brgds,

Tobi
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Tue Jan 08, 2013 6:38 am
vinni.k wrote: Why answer cannot be D. Statement (1) gives x = 0 or y = 1. It is giving x = 0. Why should we concerned about y = 1 when we are already getting x = 0 as it is being already asked ?
Good question, Vinni.

The problem is that you've reduced the strength of the question.
Yes, for statement 1, x could equal 0, but the target question doesn't ask, "Could x = 0?" The target question asks, "Does x = 0?"
In other words, "Must it be the case that x = 0?"

With all data sufficiency questions, a statement is sufficient if we are able to answer the target question with certainty.

In statement 1, we cannot answer the target question ("Does x = 0?") with absolute certainty, so it's not sufficient.

If you're interested, we have a free set of videos that cover everything you need to know about data sufficiency questions: https://www.gmatprepnow.com/module/gmat-data-sufficiency

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 421
Joined: Sun Apr 17, 2011 4:27 am
Location: India
Thanked: 6 times
Followed by:2 members
GMAT Score:620

by vinni.k » Tue Jan 08, 2013 9:17 am
Brent@GMATPrepNow wrote: Statement 1: xy = x
There are several pairs of values for x and y that meet this condition. Here are two:
Case a: x = 0 and y = 2, in which case x = 0
Case b: x = 3 and y = 1, in which case x = 3
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT
Thanks Brent. Actually i solved this question algebraically and didn't use different examples to verify the statement. This is where i make silly mistakes, and my questions get wrong and then i ask myself why my scores are not increasing. :(

Regards
Vinni
Top
Post new topic Post Reply
• Page 1 of 1