It is currently 20 Feb 2018, 15:28

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

PS-Comb

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Senior Manager
Senior Manager
avatar
Joined: 05 Jun 2008
Posts: 304
PS-Comb [#permalink]

Show Tags

New post 02 Dec 2008, 04:00
1
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

100% (00:02) correct 0% (00:00) wrong based on 3 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

How many 5-digit positive integers exist where no two consecutive digits are the same?

A.) 9*9*8*7*6
B.) 9*9*8*8*8
C.) 9^5
D.) 9*8^4
E.) 10*9^4
Current Student
avatar
Joined: 28 Dec 2004
Posts: 3342
Location: New York City
Schools: Wharton'11 HBS'12
Re: PS-Comb [#permalink]

Show Tags

New post 02 Dec 2008, 09:30
i get C as well

first integer is 9 ways, second integer 9 also, includes 0, so now the next we can continue the same 9^5
Senior Manager
Senior Manager
avatar
Joined: 05 Jun 2008
Posts: 304
Re: PS-Comb [#permalink]

Show Tags

New post 03 Dec 2008, 04:48
scthakur wrote:
I think the answer should be A.

The first place has 9 possibilities, since 0 is not to be counted. All others have 9 each, since you cannot have the digit, which is same as the preceding one.
Hence 9^5
SVP
SVP
avatar
Joined: 17 Jun 2008
Posts: 1529
Re: PS-Comb [#permalink]

Show Tags

New post 04 Dec 2008, 02:46
vivektripathi wrote:
scthakur wrote:
I think the answer should be A.

The first place has 9 possibilities, since 0 is not to be counted. All others have 9 each, since you cannot have the digit, which is same as the preceding one.
Hence 9^5


Oh, my silly analysis!

Thanks Vivek.
Intern
Intern
User avatar
Joined: 01 Nov 2005
Posts: 47
Location: New jersey
Re: PS-Comb [#permalink]

Show Tags

New post 04 Dec 2008, 03:27
Whats the OA. i would think the answer would be since it is 5 digits .

first digit is going to be from 0..9
second digit is going to be one option less then 0..9
third .. (same as first two ) and so forth.

10*9*8*7*6

Curious to know the OA and explanation.
_________________

Target +700
Life is like a box of chocolate, you never know what you gonna get.. :)

Senior Manager
Senior Manager
avatar
Joined: 30 Nov 2008
Posts: 483
Schools: Fuqua
Re: PS-Comb [#permalink]

Show Tags

New post 04 Dec 2008, 08:33
I guess the answer would be D - 9 * 8^4 And here is the explanation

Let _ _ _ _ _ be five digits positive integers (Means they can range from 1 to 9. I call them as first digit, second digit etc starting from Left side.

So the first digit can be picked from 9 positive integers = 9
Since no two consecutive digits should be same, second digit can be picked from 8 different numbers(eliminating the number picked from first digit = 8
Similary third, fourth and fifth digits can be picked from 8 different numbers each(eliminating the number picked from previous digit ).

So the answer is 9 * 8 * 8 * 8 * 8 = 9 * 8^4.
SVP
SVP
User avatar
Joined: 29 Aug 2007
Posts: 2467
Re: PS-Comb [#permalink]

Show Tags

New post 04 Dec 2008, 09:07
mrsmarthi wrote:
I guess the answer would be D - 9 * 8^4 And here is the explanation

Let _ _ _ _ _ be five digits positive integers (Means they can range from 1 to 9. I call them as first digit, second digit etc starting from Left side.

So the first digit can be picked from 9 positive integers = 9
Since no two consecutive digits should be same, second digit can be picked from 8 different numbers(eliminating the number picked from first digit = 8
Similary third, fourth and fifth digits can be picked from 8 different numbers each(eliminating the number picked from previous digit ).

So the answer is 9 * 8 * 8 * 8 * 8 = 9 * 8^4.


First digit from 1 to 9 = 9 ways
Second digit from 0 to 9 but exclude one that is already in first digit = 9 ways
Third digit from 0 to 9 but exclude one that is already in second digit = 9 ways
Fourth digit is also from 0 to 9 but exclude one that is already in third digit = 9 ways
Fifth (final) digit is also from 0 to 9 but exclude one that is already in fourth digit = 9 ways

So the possibilities are 9x9x9x9x9 = 9^5 ways..


vivektripathi wrote:
How many 5-digit positive integers exist where no two consecutive digits are the same?

A.) 9*9*8*7*6
B.) 9*9*8*8*8
C.) 9^5
D.) 9*8^4
E.) 10*9^4

_________________

Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

Senior Manager
Senior Manager
avatar
Joined: 30 Nov 2008
Posts: 483
Schools: Fuqua
Re: PS-Comb [#permalink]

Show Tags

New post 04 Dec 2008, 12:09
I have given my guess based on the fact that it is 5 digit positive integers. So my understanding is all the 5 digits can be positive integers in other words 1 to 9. O is neither positive or negative.

Any official answer???
SVP
SVP
User avatar
Joined: 29 Aug 2007
Posts: 2467
Re: PS-Comb [#permalink]

Show Tags

New post 04 Dec 2008, 13:49
mrsmarthi wrote:
I have given my guess based on the fact that it is 5 digit positive integers. So my understanding is all the 5 digits can be positive integers in other words 1 to 9. O is neither positive or negative.

Any official answer???



You are talking about a single digit where as the question is about 5 digit integer.
Suppose if 10,101 is a 5 digit +ve integer, -10,101 is a 5 digit -ve integer.

This is what meant by the +ve and -ve integer in the question.
_________________

Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

Re: PS-Comb   [#permalink] 04 Dec 2008, 13:49
Display posts from previous: Sort by

PS-Comb

  post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.