GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 17 Aug 2018, 10:09

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

If each term in the sum A1+A2+ An is either 7 or 77 and the

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Intern
Intern
avatar
Joined: 25 Dec 2008
Posts: 41
If each term in the sum A1+A2+ An is either 7 or 77 and the  [#permalink]

Show Tags

New post 01 Jan 2009, 12:49
If each term in the sum A1+A2+………An is either 7 or 77 and the sum equals 350, which of the following could be equal to n?
A. 38
B. 39
C. 40
D. 41
E. 42

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
SVP
SVP
User avatar
Joined: 29 Aug 2007
Posts: 2420
Re: series  [#permalink]

Show Tags

New post 01 Jan 2009, 13:51
shobuj40 wrote:
If each term in the sum A1+A2+………An is either 7 or 77 and the sum equals 350, which of the following could be equal to n?
A. 38
B. 39
C. 40
D. 41
E. 42



C. Since 77 = 11(7), n = 50 because 350 = 7n.

1. 77 (0) + 7 (50) = 350 ...........total terms = 50.
2. 77 (1) + 7 (39) = 350 ........... total terms = 40
3. 77 (2) + 7 (28) = 350 ............ total terms = 30.

Since number of terms in ACs are all over 38 but smaller than 50, it should be 39+1 = 40 in C.
_________________

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

VP
VP
avatar
Joined: 17 Jun 2008
Posts: 1474
Re: series  [#permalink]

Show Tags

New post 02 Jan 2009, 04:48
Another approach:

7x + 77y = 350
or, x + 11y = 50
or, y = (50-x)/11 and in order for y to be aninteger, (50-x) is to be a multiple of 11.

i.e., (50-x) could be 11, 22, 33, 44
or, x could be 39, etc.
and hence, y could be 1, etc.

Hence, n = x + y = 40, etc.
GMAT Tutor
avatar
S
Joined: 24 Jun 2008
Posts: 1345
Re: series  [#permalink]

Show Tags

New post 02 Jan 2009, 11:36
1
Or just look at the units' digit: we're adding a lot of numbers that end in 7, and we're getting something ending in 0. That could only happen if we're adding 10, or 20, or 30, etc, numbers together; the number of numbers must be a multiple of 10. So 40 must be the answer.

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

_________________

GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Re: series &nbs [#permalink] 02 Jan 2009, 11:36
Display posts from previous: Sort by

If each term in the sum A1+A2+ An is either 7 or 77 and the

  post reply Question banks Downloads My Bookmarks Reviews Important topics  

Moderator: chetan2u

Events & Promotions

PREV
NEXT


GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| 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®.