BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

Sequence Problem

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 52
Joined: Sat Aug 14, 2010 9:24 pm
by vongdn » Wed Oct 06, 2010 7:59 pm
If each term in the sum a1+a2+a3+...+an is either 7 or 77 and the sum = 350, which of the following could be equal to n?

38
39
40
41
42


Answer is 40

Is this because the only way that the sums of 7 and 77 can come up to 350 is if they add up to a sum that ends in 0, and that the only multiple of 7 that ends in 0 is if it were multiplied by 10?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 1179
Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members
Location: Milpitas, CA
Thanked: 447 times

by Rahul@gurome » Wed Oct 06, 2010 8:12 pm
If each term in the sum a1+a2+a3+...+an is either 7 or 77 and the sum = 350, which of the following could be equal to n?

Let the number of terms which are 77 be x.
So number of terms which are 7 is (n-x).
Or 77x + 7(n-x) = 350.
Or 70x + 7n = 350.
Or n = 50 -10x.
Note that n and x are non negative integers. Also n is more than 0. So 50 -10x > 0 or x < 5.
Now if x is 1, n = 40.

So n can take the value of 40.
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Wed Oct 06, 2010 8:16 pm
vongdn wrote:If each term in the sum a1+a2+a3+...+an is either 7 or 77 and the sum = 350, which of the following could be equal to n?

38
39
40
41
42


Answer is 40

Is this because the only way that the sums of 7 and 77 can come up to 350 is if they add up to a sum that ends in 0, and that the only multiple of 7 that ends in 0 is if it were multiplied by 10?
350/7 = 50. So if each term were 7, we'd have 50 terms. The answer choices are all a little less than 50. So most -- but not all -- of the terms will be 7.

If 1 term = 77, we have 350-77 = 273 left.
273/7 = 39. This works!
So 1 term = 77, 39 terms = 7.
Total number of terms is 1+39 = 40.

The correct answer is C.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 250
Joined: Thu Jan 07, 2010 2:21 am
Thanked: 10 times

by saurabhmahajan » Wed Oct 06, 2010 11:06 pm
GMATGuruNY,

I have seen many of your posts where you have solved by plugging numbers and inspired form that i have also solved many of the problems on this forum the same way as you did.

Thanks for helping me and inspiring me.
Keep posting.
Thanks and regards,
Saurabh Mahajan

I can understand you not winning,but i will not forgive you for not trying.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
GMAT Instructor
Posts: 1302
Joined: Mon Oct 19, 2009 2:13 pmFollowed by: 164 members
Location: Toronto
Thanked: 539 times
GMAT Score:800

by Testluv » Thu Oct 07, 2010 2:31 am
Is this because the only way that the sums of 7 and 77 can come up to 350 is if they add up to a sum that ends in 0, and that the only multiple of 7 that ends in 0 is if it were multiplied by 10?
...yes!!! That's also the fastest way to solve this problem:

There's eleven 7s in 77. So how can a bunch of 7s sum to 350? Well, since 350 ends in "0", the number of 7s must be a multiple of 10. Only one choice is a multiple of 10--choice C!
Kaplan Teacher in Toronto
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Fri Oct 08, 2010 10:44 am
saurabhmahajan wrote:GMATGuruNY,

I have seen many of your posts where you have solved by plugging numbers and inspired form that i have also solved many of the problems on this forum the same way as you did.

Thanks for helping me and inspiring me.
Keep posting.
I'm glad that you've been finding my posts helpful. It's my goal -- and that of The Princeton Review -- to use and teach consistent methods that can be applied to many kinds of problems. I plug in my own values or plug in the answer choices in order to solve a majority of GMAT questions.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 77
Joined: Sat Sep 25, 2010 9:45 pm

by Yanat » Fri Oct 08, 2010 10:20 pm
350-77 = 273

273/7 = 39

so we have 39+1 = 40 and so it is C.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1