OG 12; data sufficiency; problem 167

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Pugalenthi: Junior | Next Rank: 30 Posts; Posts: 29; Joined: Fri Sep 25, 2009 9:26 am

by Pugalenthi » Fri Jun 01, 2012 7:01 am

If n is a positive integer, what is the tens digit of n?
(1) the hundreds digit of 10n is 6
(2) the tens digit of n+1 is 7

The answer is A.

I can understand why B is not an answer but not able to understand why A is the answer. Any help would be much appreciated.

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Source: Beat The GMAT — Data Sufficiency | Fri Jun 01, 2012 7:01 am

Pugalenthi: Junior | Next Rank: 30 Posts; Posts: 29; Joined: Fri Sep 25, 2009 9:26 am

by Pugalenthi » Fri Jun 01, 2012 7:07 am

I found a good explanation for this...https://www.youtube.com/watch?v=wLAbFXBq ... plpp_video

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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

by Brent@GMATPrepNow » Fri Jun 01, 2012 8:10 am

Pugalenthi wrote:If n is a positive integer, what is the tens digit of n?
(1) the hundreds digit of 10n is 6
(2) the tens digit of n+1 is 7

The answer is A.

I can understand why B is not an answer but not able to understand why A is the answer. Any help would be much appreciated.

Statement 1: the hundreds digit of 10n is 6
Notice what happens when we multiply any positive integer by 10:
34 x 10 = 340
60 x 10 = 600
128 x 10 = 1280
54629 x 10 = 546290
The tens digit in the original number becomes the hundreds digit in the new number.

So, if we're told that the hundreds digit of 10n is 6, then we know that the tens digit in n must be 6.
So, statement 1 is SUFFICIENT

Statement 2: the tens digit of n+1 is 7
case a: n=69 in which case the tens digit of n is 6
case b: n=74 in which case the tens digit of n is 7
Since we can't answer the target question with certainty, statement 2 is NOT SUFFICIENT and the answer is A

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Fri Jun 01, 2012 8:11 am

Refer to the post here >> https://www.beatthegmat.com/tens-digit-o ... tml#426692

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