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.
It appears that you are browsing the GMAT Club forum unregistered!
Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club
Registration gives you:
Tests
Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.
Applicant Stats
View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more
Books/Downloads
Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!
Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
Re: GMAT CLUB - PS. (Dont agree with OE -but agree with OA) [#permalink]
21 Aug 2008, 12:18
I figured it like this: (and I realize there is a formula for this too, but I'm not sure what it is).
This method took me about 90 seconds to complete.
Answer: 300
Units Digit: 10-7's per 100 numbers * 10 groups of 100 from 1 - 1000 = 100 Tens Digit: 10-7's in the 70's section of each group of 100 so 10*10 = 100 Hundreds digit: 100-7's from 700 to 799, so 100 again
Total = 300.
Am I forgetting anything?
x2suresh wrote:
How many times will the digit 7 be written when listing the integers from 1 to 1000?
110 111 271 300 304
This problem is from GMACLUB test. I agree with answer but not the explanation.
Let see how others will tackle this problem.
_________________
------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.
Re: GMAT CLUB - PS. (Dont agree with OE -but agree with OA) [#permalink]
21 Aug 2008, 12:52
When counting the times a certain number appears, this might be a more scientific method of counting.
If you're counting units digits, you know that any single number will appear in the units digit column 1 time out of 10. If you're counting 1 to n, then multiply the number of times that digit appears out of 10 * n/10: Example: looking for # of 5s in the units column from 1 to 600. There will be a 5 in each group of 10. So take 600 (the 1 to 600) and divide 600 by 10, for 60. There will be 60-5's in the units column from 1 to 600.
Tens column: You see there will be 10-5's in the tens column per group of 100. Divide the last number by the size of the group. 600 / 100 = 6 groups, so 60-50s in the tens digit.
Hundreds column: You know there will be 5's here only in 500-599. So that's 100 numbers per group of 1000. Since we don't go all the way to 1000, we know that's 1. so It's 100*1. what's the total? 60+60+100 = 220.
LOL....I'm not sure this makes it any easier!!
hibloom wrote:
I got D with similar counting method and took about 90 sec But I would love to know some shorter method
_________________
------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.
Re: GMAT CLUB - PS. (Dont agree with OE -but agree with OA) [#permalink]
21 Aug 2008, 13:10
x2suresh wrote:
zoinnk wrote:
x2suresh wrote:
How many times will the digit 7 be written when listing the integers from 1 to 1000?
110 111 271 300 304
This problem is from GMACLUB test. I agree with answer but not the explanation.
Let see how others will tackle this problem.
For every 100 numbers, 7 appears 10 times (x07, x17, x27, x37, x47, x57, x67, x77, x87, x97) --> Do you belieive 7 appeared 10 times or 11 times here. Don't worry your answer is correct.. Here you treated x77 (7 in the 10th place ignored.. and reconsider when "Ten digit calculations" ) 10*10 = 100
Tens digit: For every 100 numbers, 7 appears 10 times (x70, x71, x72, x73, x74, x75, x76, x77, x78, x79) 10*10 = 100
Hundreds digit: 7 appears in the hundreds digit in every number from 700-799 799-700+1 = 100
Total 7s: 100+100+100 = 300
I ignored the 7 in the tens place for that part of the calculation because i was just counting the 7s in the ones digit.
Re: GMAT CLUB - PS. (Dont agree with OE -but agree with OA) [#permalink]
21 Aug 2008, 13:14
Hi Allen and Zoink,
Agree with both of you.. Now I agree with OE approach too.. OE is also explained similar to your approach. ( You ignored the x77 tenth digit 7 when counting unit digit calculations and reconsider this 7 when tenth digit calucations.. see zoink reply)
My approach was:
7 occur only once. (7XX, X7X,XX7) = "7 is one of the digit" * "select other than 7" * "select other than 7" * (no of ways 7 can appear ) = 1*9*9* 3 =243 7 occur twice (77X,7X7,X77) = "7 is two of the digit" * "select 3rd one other than 7" * ( Each number 7 written twice)