Forum Home > GMAT > Quantitative > Problem Solving (PS)
Events & Promotions
|
|
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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Jan 1810:00 AM PST
-11:00 AM PST
In this video, we talked to Rishi, an ambitious Indian student who successfully secured admission into HEC Paris and ESSEC Business School, two of the top Masters in Management (MiM) programs in Europe.
Jan 1911:00 AM IST
-01:00 PM IST
Attend this session to evaluate your current skill level, learn process skills, and solve through tough Arithmetic questions- Jan 20
12:01 AM PST
-11:59 PM PST
On Monday the 20th GMAT Club Tests will be Absolutely Free! Including all the Quizzes, Questions, and Tests. 12 AM - 11:59 PM PST - Jan 20
10:00 AM PST
-11:00 AM PST
Join us for an inspiring talk with Dhruvi, an ambitious Indian student who secured admission to Imperial College London's prestigious Masters in Management (MiM) program. In this podcast, Dhruvi shares her candid journey... - Jan 21
09:00 AM PST
-10:00 AM PST
If you're aiming for top MBA programs like Stanford, Harvard, or Wharton, this video is your ultimate guide to crafting a standout application that B-schools can't ignore! We'll walk you through: - Jan 22
08:00 AM PST
-09:00 AM PST
In this video, two MBA interview experts and a communications coach holds a mock interview of a prospective MBA applicant. The experts assess the responses of the applicant on important interview questions and provide their feedback. 
Jan 2410:00 AM EST
-12:00 PM EST
The Target Test Prep team is proud to introduce GMAT OnDemand, a video course created by Scott Woodbury-Stewart, founder and CEO, designed to provide you with everything you need to master the GMAT and achieve your score goals.
10 May 2010, 09:36
Kudos
Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
35%
(medium)
Question Stats:
75% (01:55) correct
25%
(02:07)
wrong
based on 4939
sessions
History
Date
Time
Result
Not Attempted Yet
If each term in the sum \(a_1+a_2+a_3+...+a_n\) 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
A. 38
B. 39
C. 40
D. 41
E. 42
26 Dec 2010, 02:36
Kudos
Bookmarks
If each term in the sum \(a_1+a_2+a_3+...+a_n\) 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
Number of approaches are possible.
For example, approach #1:
Since the units digit of 350 is zero then the number 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.
Approach #2:
\(7x+77y=350\), 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.
Answer: C.
Hope it helps.
A. 38
B. 39
C. 40
D. 41
E. 42
Number of approaches are possible.
For example, approach #1:
Since the units digit of 350 is zero then the number 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.
Approach #2:
\(7x+77y=350\), 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.
Answer: C.
Hope it helps.
If each term in the sum \(a_1+a_2+a_3+...+a_n\) 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
\(350 \ can \ be \ comprised \ of \ 7 \ but \ not \ of \ 77. \ As \ 350 \ is \ not \ a \ multiple \ of \ 77.\)
For example \(\frac{350}{7}=50\), but \(\frac{350}{77}=4.54..\) is not an integer
So \(50 \) can be an answer but it is not in the answer choices.
\(Thus \ we \ infer \ that \ there \ must \ be \ at \ least \ one \ 77 \ in \ 350\)
\(Let's \ Check\)
\(350 - 77 = 273\)
\(\frac{273}{7}= 39; \ i.e. \ 273+77=350\)
\(So, \ there \ are \ 39s 7 \ and \ one \ 77 \ in \ 350\)
\(39+1 = 40.\)
The answer is C.
A. 38
B. 39
C. 40
D. 41
E. 42
\(350 \ can \ be \ comprised \ of \ 7 \ but \ not \ of \ 77. \ As \ 350 \ is \ not \ a \ multiple \ of \ 77.\)
For example \(\frac{350}{7}=50\), but \(\frac{350}{77}=4.54..\) is not an integer
So \(50 \) can be an answer but it is not in the answer choices.
\(Thus \ we \ infer \ that \ there \ must \ be \ at \ least \ one \ 77 \ in \ 350\)
\(Let's \ Check\)
\(350 - 77 = 273\)
\(\frac{273}{7}= 39; \ i.e. \ 273+77=350\)
\(So, \ there \ are \ 39s 7 \ and \ one \ 77 \ in \ 350\)
\(39+1 = 40.\)
The answer is C.
