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: least value of N (m09q33) [#permalink]
03 Sep 2010, 04:28
7
This post received KUDOS
1000 = 2^3 x 5^3 so, we are looking for a number N such that N! contains at least 2^3 x 5^3 as factors. A. 8! = 2^3.7.6.5.4! .... only 2^3.5 wrong B. 10! = (2*5).9.8.7.6.5.4!...only 2^3.5^2 wrong, we need an additional 5. C. 15! = (3*5).(2*7).13.(2*6).11.(2*5).9.8! 2^3.5^3 is available in 15!...corect D. 20! we looking for the least- 20! is not necessary E. 25! same as option D _________________
KUDOS me if you feel my contribution has helped you.
Re: least value of N (m09q33) [#permalink]
05 Sep 2010, 08:33
1
This post received KUDOS
For such questions, always work through the answers choice from lowest to highest i.e. A to E. The moment you get an answers that matches, stop and mark that as the answer and move on.
1000 = 2^3 x 5^3 N! has to contain 2^3 x 5^3 as factors. A) 8! --> only 2^3 * 5^1 --> wrong B) 10! --> only 2^3 * 5^2 --> wrong C) 15! = --> 2^3 * 5^3 --> BINGO _________________
If you like my post, consider giving me a kudos. THANKS!
Re: least value of N (m09q33) [#permalink]
09 Sep 2010, 10:06
For the N! to be divisible by 1,000, it needs 3 5's and 3 2's in it (5^3 and 2^3). We can just look at 5's since 2's will be more abundant. There are some good posts on divisibility by factors of 10 that work out this more clearly.
As we go up from 1!, we would get a 5 in each of: 5, 10, and 15. If you want to check there are three 2's by the time you get to 4! so we're covered. 15! will be the first that is divisible by 1,000.
It might be tempting to look at 10! since you get above 100 so quickly, but 10! if 3,628,800, which /1,000 is not an integer (done in excel, not needed on the test or if you understand the concepts.
Re: least value of N (m09q33) [#permalink]
25 Oct 2011, 21:00
sarathy wrote:
For such questions, always work through the answers choice from lowest to highest i.e. A to E. The moment you get an answers that matches, stop and mark that as the answer and move on.
I would add that for "least" questions this should be done. The opposite should be done for "greatest".