Find all School-related info fast with the new School-Specific MBA Forum

It is currently 24 Oct 2014, 06:49

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

OG 11- Quant Sample- Question 11

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Senior Manager
Senior Manager
User avatar
Joined: 25 Nov 2006
Posts: 337
Schools: St Gallen, Cambridge, HEC Montreal
Followers: 2

Kudos [?]: 28 [0], given: 0

OG 11- Quant Sample- Question 11 [#permalink] New post 19 Mar 2007, 16:10
Hello,

Would anybody have a formula/explanation for this:
"Of the three-digit integers greater than 700, how many have two digits that are equal to each other and the remaining digit different from the other two?"
Senior Manager
Senior Manager
avatar
Joined: 11 Feb 2007
Posts: 360
Followers: 1

Kudos [?]: 24 [0], given: 0

 [#permalink] New post 19 Mar 2007, 16:38
This isn't a formula or a mathematical explanation but I would just go with the primitive method (I won't be able to come up with a formula in 2 minutes anyway... :? )

8xx where x = 0~7, 9 - 9 of them
8x8 where x = 0~7, 9 - 9 of them
88x where x = 0~7, 9 - 9 of them
total 27

since it would be the same for the others in 700s and 900s

27 x 3 = 81

however, since it has to be greater than 700, subtract the case 7xx where x = 0.

81 - 1 = 80

What is the OA?
(I might have missed out on something...)

This might not be what you wanted..but... :wink:
Senior Manager
Senior Manager
User avatar
Joined: 25 Nov 2006
Posts: 337
Schools: St Gallen, Cambridge, HEC Montreal
Followers: 2

Kudos [?]: 28 [0], given: 0

 [#permalink] New post 19 Mar 2007, 16:47
Thanks.

Answer is 80, so you're right.

Could you explain this more? I am not sure to get it :?


8xx where x = 0~7, 9 - 9 of them
8x8 where x = 0~7, 9 - 9 of them
88x where x = 0~7, 9 - 9 of them
Senior Manager
Senior Manager
avatar
Joined: 11 Feb 2007
Posts: 360
Followers: 1

Kudos [?]: 24 [0], given: 0

 [#permalink] New post 19 Mar 2007, 17:13
lumone wrote:
Thanks.

Answer is 80, so you're right.

Could you explain this more? I am not sure to get it :?


8xx where x = 0~7, 9 - 9 of them
8x8 where x = 0~7, 9 - 9 of them
88x where x = 0~7, 9 - 9 of them


8xx where x = 0~7, 9 - 9 of them
-> Keep the 8 fixed and make the ten's and unit's digits the same. For example, 800, 811, 822, etc. However, you cannot have 8xx where x = 8 since then, there would be 3 (not 2) identical numbers.

8x8 where x = 0~7, 9 - 9 of them
-> Keep the hundred's and unit's digits fixed and rotate the middle digits.

88x where x = 0~7, 9 - 9 of them
-> Keep the first two digits fixed and rotate the last digits.

:-D
Manager
Manager
avatar
Joined: 12 Feb 2007
Posts: 167
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 19 Mar 2007, 17:32
What am I doing wrong here?

I used a brute force method,

700
707
711
717

so every change in the tens digit, there are 2 possibilities, except for 77x where there are 10 possibilities, so therefore there are 26 possibilities for the 700's, same of 800's and the 900's, so

26*3=78
Senior Manager
Senior Manager
avatar
Joined: 11 Feb 2007
Posts: 360
Followers: 1

Kudos [?]: 24 [0], given: 0

 [#permalink] New post 19 Mar 2007, 18:00
Tuneman wrote:
What am I doing wrong here?

I used a brute force method,

700
707
711
717

so every change in the tens digit, there are 2 possibilities, except for 77x where there are 10 possibilities, so therefore there are 26 possibilities for the 700's, same of 800's and the 900's, so

26*3=78


Hi Tuneman,

You shouldn't include 700 cuz it said that the number is greater than 700. More important, 77x does not have 10 possibilities because 777 would have three identical numbers instead of two.
CEO
CEO
User avatar
Joined: 21 Jan 2007
Posts: 2769
Location: New York City
Followers: 8

Kudos [?]: 255 [0], given: 4

Re: [#permalink] New post 07 Jan 2008, 13:09
ricokevin wrote:
This isn't a formula or a mathematical explanation but I would just go with the primitive method (I won't be able to come up with a formula in 2 minutes anyway... :? )

8xx where x = 0~7, 9 - 9 of them
8x8 where x = 0~7, 9 - 9 of them
88x where x = 0~7, 9 - 9 of them
total 27

since it would be the same for the others in 700s and 900s

27 x 3 = 81

however, since it has to be greater than 700, subtract the case 7xx where x = 0.

81 - 1 = 80

What is the OA?
(I might have missed out on something...)

This might not be what you wanted..but... :wink:

thanks. very helpful
_________________

You tried your best and you failed miserably. The lesson is 'never try'. -Homer Simpson

Re:   [#permalink] 07 Jan 2008, 13:09
    Similar topics Author Replies Last post
Similar
Topics:
OG 11 Number of questions? Crow 2 15 Nov 2007, 03:45
OG11 question difficulty pmenon 3 12 Aug 2007, 11:58
OG11 PS Question lonesome307 1 09 Aug 2007, 14:13
OG 11- Quant Sample- Question 15 lumone 6 19 Mar 2007, 16:40
OG 11 question guide baer 2 02 Sep 2006, 20:55
Display posts from previous: Sort by

OG 11- Quant Sample- Question 11

  Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group and phpBB SEO

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®.