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: 7,77....Problem Solving [#permalink]
23 Mar 2006, 02:58
11
This post received KUDOS
lhotseface wrote:
If each term in the sum a1 + a2 + a3.....+ an is either 7 or 77 and the sum is 350, What is n ?
Note: a1,a2 represent the first term,second...and NOT a*1, a*2 !
A. 38 B. 39 C. 40 D. 41 E. 42
Let x and y be the number of term 7 and the number of term 77 respectively. WE have :
7x+ 77y= 350 ---> x+11y = 50 ---> x+y= 50- 10y
we have : x+y= n = 50- 10y ---> n must have the unit digit of 0 because 50 - 10y must be a number which has unit digit of 0
Among the answer choices provided, only C matches.
For example: as units digit of 350 is zero then # of terms must be multiple of 10. Only answer choice which is multiple of 10 is C (40).
To illustrate consider adding:
*7 *7 ... 77 77 ---- =350
So, several 7's and several 77's, note that the # of rows equals to the # of terms. Now, to get 0 for the units digit of the sum the # of rows (# of terms) must be multiple of 10. Only answer choice which is multiple of 10 is C (40).
Answer: C.
Or: \(7x+77y=350\), where \(x\) is # of 7's and \(y\) is # of 77's, so # of terms \(n\) equals to \(x+y\);
\(7(x+11y)=350\) --> \(x+11y=50\) --> now, if \(x=39\) and \(y=1\) then \(n=x+y=40\) and we have this number in answer choices.
Re: 7,77....Problem Solving [#permalink]
28 Jun 2011, 08:51
laxieqv wrote:
lhotseface wrote:
If each term in the sum a1 + a2 + a3.....+ an is either 7 or 77 and the sum is 350, What is n ?
Note: a1,a2 represent the first term,second...and NOT a*1, a*2 !
A. 38 B. 39 C. 40 D. 41 E. 42
Let x and y be the number of term 7 and the number of term 77 respectively. WE have : 7x+ 77y= 350 ---> x+11y = 50 ---> x+y= 50- 10y we have : x+y= n = 50- 10y ---> n must have the unit digit of 0 because 50 - 10y must be a number which has unit digit of 0
Among the answer choices provided, only C matches.
Re: 7,77....Problem Solving [#permalink]
29 Jun 2011, 16:29
1
This post was BOOKMARKED
laxieqv wrote:
lhotseface wrote:
If each term in the sum a1 + a2 + a3.....+ an is either 7 or 77 and the sum is 350, What is n ?
Note: a1,a2 represent the first term,second...and NOT a*1, a*2 !
A. 38 B. 39 C. 40 D. 41 E. 42
Let x and y be the number of term 7 and the number of term 77 respectively. WE have : 7x+ 77y= 350 ---> x+11y = 50 ---> x+y= 50- 10y we have : x+y= n = 50- 10y ---> n must have the unit digit of 0 because 50 - 10y must be a number which has unit digit of 0
Among the answer choices provided, only C matches.
I go for C.
I like this method because it attacks the the question dead on by representing each term as x and y and then deductively finding the answer through POE. Hope I can think this quickly on the exam!
I used a different method altogether. I observed that since all the numbers are 7s, the total number of sevens has to be a multiple of 5 in order to get to 350. out of the answer choices, only 40 is a multiple of 5, So eliminate everything but choice C. I guess, if there were other multiples of 5 then you could use one of the methods above. But as a quick elimination strategy it helped to do the least amount of work.
+1 C 7(50)=350 Since 50 is not there in ANSWERS so 77 needs to be ther 77=7(11) So : number of terms if one 77 is there 50-11+1=50-10=40 --> Check the Ans. C matches.. _________________
Re: If each term in the sum a1 + a2 + a3.....+ an is either 7 or [#permalink]
30 Oct 2013, 03:23
Hello from the GMAT Club BumpBot!
Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).
Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________
The “3 golden nuggets” of MBA admission process With ten years of experience helping prospective students with MBA admissions and career progression, I will be writing this blog through...
You know what’s worse than getting a ding at one of your dreams schools . Yes its getting that horrid wait-listed email . This limbo is frustrating as hell . Somewhere...