If x is a non-negative integer then find x?(Source:GMATINSIG

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GMATinsight: Legendary Member; Posts: 1100; Joined: Sat May 10, 2014 11:34 pmFollowed by: 24 members; Location: New Delhi, India; Thanked: 205 times

by GMATinsight » Mon Oct 17, 2016 4:13 am

If x is a Non-Negative integer then find x?
(1) x^2âˆ’5x+6=0
(2) x^2=3x

(Source:www.GMATinsight.com)

Answer: option C

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Source: Beat The GMAT — Data Sufficiency | Mon Oct 17, 2016 4:13 am

melguy: Master | Next Rank: 500 Posts; Posts: 335; Joined: Mon Mar 21, 2011 11:31 pmFollowed by: 2 members; Location: Australia / India; Thanked: 37 times

by melguy » Mon Oct 17, 2016 5:19 am

1) x^2-5x+6=0
(x-3) (x-2) = 0
x = 3 or x = 2
Not Sufficient

2) x^2=3x
Divide both sides by x
x = 3
Sufficient

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GMATinsight: Legendary Member; Posts: 1100; Joined: Sat May 10, 2014 11:34 pmFollowed by: 24 members; Location: New Delhi, India; Thanked: 205 times

by GMATinsight » Mon Oct 17, 2016 5:46 am

melguy wrote:1) x^2-5x+6=0
(x-3) (x-2) = 0
x = 3 or x = 2
Not Sufficient

2) x^2=3x
Divide both sides by x
x = 3
Sufficient

You answer is Incorrect because of a small mistake that you have made while solving the second statement

x^2=3x
You CAN'T divide both sides by x because x may be zero as well. You can only divide an equation by a variable when you know it's non zero

therefore, x^2=3x
i.e. x^2-3x = 0
i.e. x (x-3) = 0
i.e. x = 0 or 3 i.e.
NOT SUFFICIENT

Combining both statements
x=3
SUFFICIENT

Answer: Option C

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GMAT/MBA Expert

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

by Brent@GMATPrepNow » Mon Oct 17, 2016 7:06 am

NOTE: when we're told that a number is "non-negative," we must be careful not to conclude that the number is positive.
A non-negative number can be positive or it can equal 0

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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melguy: Master | Next Rank: 500 Posts; Posts: 335; Joined: Mon Mar 21, 2011 11:31 pmFollowed by: 2 members; Location: Australia / India; Thanked: 37 times

by melguy » Mon Oct 17, 2016 8:03 am

Brent@GMATPrepNow wrote:NOTE: when we're told that a number is "non-negative," we must be careful not to conclude that the number is positive.
A non-negative number can be positive or it can equal 0

Cheers,
Brent

My bad!

Thanks for correcting me.

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