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

It is currently 28 Nov 2014, 22:18

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

Challenges 1, Q10

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Intern
Intern
avatar
Joined: 22 Mar 2007
Posts: 1
Followers: 0

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

Challenges 1, Q10 [#permalink] New post 25 May 2011, 00:59
Hi, have problem with such kinde of questions. Maybe somebody has another explanation. Or it is possible to finde a topic in Manhattan Guides.
Thank you.

How many times will the digit 7 be written when listing the integers from 1 to 1000?

(C) 2008 GMAT Club - m01#10

110
111
271
300
304
There are several ways to count the number of times 7 appears between 7 and 997. One way is to consider the number of 7's in single, double, and triple digit numbers separately.

One-digit numbers: 7 is the only one-digit number.

Two-digit numbers: 7 could be the first digit or the second digit. Case 1: 7 is the first digit. There are 9 ways to place 7 as the first digit of a two-digit number. Case 2: There are 10 ways to place the second digit, i.e. 0-9. Remember that we have counted 07 already. Thus, for two-digit numbers we have: numbers that contain a 7.

Three-digit numbers: Use the knowledge from the previous two scenarios: each hundred numbers will contain one 7 in numbers such as 107 or 507 and also 19 other sevens in numbers such as 271 or 237. Thus a total of 20 sevens per each hundred and 200 sevens for 1000. Since we have 700's within the range, that adds another 100 times that a seven will be written for a total of 300 times.

The correct answer is D.
Kaplan Promo CodeKnewton GMAT Discount CodesManhattan GMAT Discount Codes
Expert Post
4 KUDOS received
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3575
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 378

Kudos [?]: 1920 [4] , given: 359

GMAT ToolKit User Premium Member
Re: Challenges 1, Q10 [#permalink] New post 25 May 2011, 07:20
4
This post received
KUDOS
Expert's post
another way:

1. The number of 7s is the same in 000-999 as in 1-1000.
2. There is 1000 numbers and 3000 digits in 000-999
3. All digits (0-9) appear with the same probability - 1/10
4. So, 7 is written 3000*1/10 = 300 times
_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

Intern
Intern
avatar
Joined: 18 May 2011
Posts: 18
Followers: 0

Kudos [?]: 2 [0], given: 1

Re: Challenges 1, Q10 [#permalink] New post 27 May 2011, 17:07
Thanks a lot Walker.... it was quite difficult but you made it easy to understand...
Intern
Intern
avatar
Joined: 30 Jan 2011
Posts: 2
Followers: 0

Kudos [?]: 0 [0], given: 5

Re: Challenges 1, Q10 [#permalink] New post 02 Sep 2011, 13:33
walker wrote:
another way:

1. The number of 7s is the same in 000-999 as in 1-1000.
2. There is 1000 numbers and 3000 digits in 000-999
3. All digits (0-9) appear with the same probability - 1/10
4. So, 7 is written 3000*1/10 = 300 times



just wanted someone to clarify, how are there 3000 digits in 000-999

awaiting a reply
Thanx
Expert Post
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3575
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 378

Kudos [?]: 1920 [0], given: 359

GMAT ToolKit User Premium Member
Re: Challenges 1, Q10 [#permalink] New post 03 Sep 2011, 10:04
Expert's post
There is 1000 numbers in 000-999 set ((999 - 0) + 1 = 1000) and each number consists with 3 digits: 3*1000 = 3000 digits
_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

Re: Challenges 1, Q10   [#permalink] 03 Sep 2011, 10:04
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic PS1000 Sec1 Q10 joyseychow 1 11 Feb 2009, 04:45
LSAT III sect.1 - q.10 marcodonzelli 2 26 Feb 2008, 22:18
Challenge 25 Q1 Columbia08 4 05 Nov 2007, 18:18
Q10) The mass of 1 cubic meter of a substance in 800 avenger 2 02 Oct 2007, 12:18
Challenge 1 - Q27 deowl 15 09 Jun 2006, 03:18
Display posts from previous: Sort by

Challenges 1, Q10

  Question banks Downloads My Bookmarks Reviews Important topics  

Moderators: WoundedTiger, Bunuel



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®.