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

Redeem

Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

★★★★★5.0559 reviews
GMATLiveTeach 7 seats left
Chris Peckover
NEXT LIVE COHORT

Oct 13 to Jan 7, 2027

with Chris Peckover

Schedule
Tue, Thu · 8:00 to 10:00 PM ET
Included
40 live hours + 6 months of GMAT OnDemand
  • Live instruction and real-time questions
  • Class recordings and assigned practice
View class & enroll
Limited cohort · enrollment openTarget Test Prep
EALiveTeach 5 seats left
Logan Thompson
EXECUTIVE ASSESSMENT

Sep 6 to Dec 6, 2026

with Logan Thompson

Schedule
Sun · 9:30 AM to 12:30 PM ET
Included
Live EA class + 6 months of EA OnDemand
  • Expert-led weekly online sessions
  • EA Masterclass access between classes
View EA class & enroll
Limited cohort · enrollment openTarget Test Prep
GMATOnDemand Start anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

130-point score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 559 reviewsTarget Test Prep

Compare the format, schedule, and included access before enrolling. Prices and seat counts shown reflect the supplied offer details.

In a sequence, each term is obtained ..

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 70
Joined: Mon Mar 30, 2009 9:00 am
Thanked: 2 times
by figs » Tue May 26, 2009 5:52 am
In a sequence, each term is obtained by adding 4 to the preceding one. If the sum of the first 10 terms is equal to 80, what is the result of the addition of the first 40 terms?
A. 94
B. 320
C. 2,720
D. 27,200
E. 54,400

can anyone explain the procedure? what's about the sum of a aritmetic sequence?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 472
Joined: Sun Mar 29, 2009 6:54 pm
Thanked: 56 times

by ssmiles08 » Tue May 26, 2009 6:44 am
The formula for the sum of the first n terms is (n/2)(2a + (n-1)*d)

where a = the first term
d = difference

So we first have to figure out a. (10/2)[2*a + (9*4)] = 80; a = -10

we use the same formula to figure out the sum of the first 40 terms

s = (40/2)[2*(-10) + (39*4)] = 2720
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 101
Joined: Tue Apr 07, 2009 12:30 am
Thanked: 2 times
GMAT Score:750

by Svedankae » Thu Jun 04, 2009 11:47 pm
I dont really get the formula, however i have an alternative suggestion... you can think of it this way.

x
+ (x+4)
+ (x+4+4)
+ (x+4+4+4)
... and so on
= 80

So if you put it more simply this becomes: 10*x +(9*5)*4 = 80

(if 9*5 is not obvious to you try to think about how many fours there will be in all ten lines... you will end up at 45)


==> x = -10


So for the first 40 lines that means:

40*x + (39*20)*4 = 2,720

(Again 39*20 is the number of all the fours that there will be in the 40 lines. I thought about it as an average. There are 39 lines in which fours make an appereance. On average (since its always one more four than in the line before) there are 20 fours. Since average * number of terms = total you end up at 39*20.


Hope that was clear. :-)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1