Last visit was: 24 Apr 2026, 13:48 It is currently 24 Apr 2026, 13:48
Home
Messages
Tests
Schools
Events
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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
User avatar
Gnpth
User avatar
Joined: 29 Aug 2012
Last visit: 03 Mar 2023
Posts: 1,039
Own Kudos:
6,774
 [20]
Given Kudos: 330
Status:Chasing my MBB Dream!
Location: United States (DC)
WE:General Management (Aerospace and Defense)
Products:
My Reviews
Posts: 1,039
Kudos: 6,774
 [20]
In the sequence a1, a2, ... , an each term after the first term is Updated on: 11 Nov 2017, 18:44
Originally posted by Gnpth on 10 Nov 2017, 19:26.
Last edited by Gnpth on 11 Nov 2017, 18:44, edited 2 times in total.
formatted the choices
1
Kudos
Add Kudos
19
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
A
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:

77% (02:23) correct 23% (02:25) wrong based on 416 sessions

History

Date
Time
Result
Not Attempted Yet
In the sequence \(a_1\), \(a_2\), ... ,\(a_n\) each term after the first term is equal to the preceding term plus a constant c.

\(a_1\) + \(a_{11}\) + \(a_{21}\) = 99. What is the value of \(a_3\)+\(a_{19}\)?

A. 66
B. 44
C. 33
D. 22
E. 11
ShowHide Answer
Official Answer
A
Most Helpful Reply
User avatar
rahul16singh28
User avatar
Joined: 31 Jul 2017
Last visit: 09 Jun 2020
Posts: 428
Own Kudos:
503
 [6]
Given Kudos: 752
Location: Malaysia
Schools: INSEAD Jan '19
GPA: 3.95
WE:Consulting (Energy)
Schools: INSEAD Jan '19
Posts: 428
Kudos: 503
 [6]
In the sequence a1, a2, ... , an each term after the first term is 10 Nov 2017, 20:26
3
Kudos
Add Kudos
3
Bookmarks
Bookmark this Post
Gnpth
In the sequence \(a_1\), \(a_2\), ... ,\(a_n\) each term after the first term is equal to the preceding term plus a constant c.

\(a_1\) + \(a_{11}\) + \(a_{21}\) = 99. What is the value of \(a_3\)+\(a_{19}\)?

A. 66
B. 44
C. 33
D. 22
E. 11
Show more

a2 = a1 + c, a3 = a2+c = a1+2c
a11 = a1+10C, a21 = a1+20c
3a1 + 30c = 99, a1+10c =33

a3+a19 = 2a1+20c = 2(a1+10c)=66
General Discussion
User avatar
chetan2u
User avatar
GMAT Expert
Joined: 02 Aug 2009
Last visit: 24 Apr 2026
Posts: 11,229
Own Kudos:
45,009
 [1]
Given Kudos: 335
Status:Math and DI Expert
Location: India
Concentration: Human Resources, General Management
GMAT Focus 1: 735 Q90 V89 DI81
Products:
My Reviews
Expert
Expert reply
GMAT Focus 1: 735 Q90 V89 DI81
Posts: 11,229
Kudos: 45,009
 [1]
In the sequence a1, a2, ... , an each term after the first term is 10 Nov 2017, 20:09
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
Gnpth
In the sequence \(a_1\), \(a_2\), ... ,\(a_n\) each term after the first term is equal to the preceding term plus a constant c.

\(a_1\) + \(a_{11}\) + \(a_{21}\) = 99. What is the value of \(a_3\)+\(a_{19}\)?

A. 33
B. 66
C. 22
D. 44
E. 11
Show more

Hi..

As each term is C more than the previous one...
Each term, \(a_x\) will be (x-1) times c more than \(a_1\)
So \(a_1+a_{11}+a_{21}=a_1+a_1+(11-1)+a_1+(21-1)=3*a_1+30=99....a_1=23\)

Now \(a_3+a_{19}=a_1+(3-1)+a_1+(19-1)=2*a_1+20=2*23+20=66\)

B

But the choices require formatting as per the GMAT. All choices are to be some order then 66 becomes choice A
User avatar
jfranciscocuencag
User avatar
Joined: 12 Sep 2017
Last visit: 17 Aug 2024
Posts: 227
Own Kudos:
144
 [3]
Given Kudos: 132
Posts: 227
Kudos: 144
 [3]
In the sequence a1, a2, ... , an each term after the first term is 18 Feb 2019, 18:39
2
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
Pn = Pn-1 + C (constant)

It is an arithmetic progression:

Sum = (Average)(n)

A1 + A11 + A21 = 99

\(\frac{99}{3} = 33\) (Average)

Sum = (33)(2) ... 2 terms (A3 + A19)

Sum = 66

A
User avatar
Balkrishna
User avatar
Joined: 17 Aug 2018
Last visit: 13 May 2022
Posts: 48
Own Kudos:
50
Given Kudos: 308
Status:Chartered Accountant
Location: India
WE:Accounting (Consulting)
Posts: 48
Kudos: 50
In the sequence a1, a2, ... , an each term after the first term is 04 Jul 2019, 05:40
Kudos
Add Kudos
Bookmarks
Bookmark this Post
chetan2u
Gnpth
In the sequence \(a_1\), \(a_2\), ... ,\(a_n\) each term after the first term is equal to the preceding term plus a constant c.

\(a_1\) + \(a_{11}\) + \(a_{21}\) = 99. What is the value of \(a_3\)+\(a_{19}\)?

A. 33
B. 66
C. 22
D. 44
E. 11

Hi..

As each term is C more than the previous one...
Each term, \(a_x\) will be (x-1) times c more than \(a_1\)
So \(a_1+a_{11}+a_{21}=a_1+a_1+(11-1)+a_1+(21-1)=3*a_1+30=99....a_1=23\)

Now \(a_3+a_{19}=a_1+(3-1)+a_1+(19-1)=2*a_1+20=2*23+20=66\)

B

But the choices require formatting as per the GMAT. All choices are to be some order then 66 becomes choice A
Show more


Why C has been assumed as 1?

Thanks
User avatar
dhruvadityajain
User avatar
Joined: 01 Dec 2022
Last visit: 03 Sep 2023
Posts: 6
Own Kudos:
7
Given Kudos: 12
Status:online
Affiliations: -------
Location: India
---: ----
Concentration: Real Estate, Sustainability
GPA: 3
WE:Architecture (Real Estate)
Posts: 6
Kudos: 7
In the sequence a1, a2, ... , an each term after the first term is 16 May 2023, 06:48
Kudos
Add Kudos
Bookmarks
Bookmark this Post
let A1 = a
A2 = a + c
A3 = a + 2c ( each term after the first term is equal to the preceding term plus a constant c.)
.
.
An = a + (n-1)xc ( Nth Term )

A1 = a ,
A11 = a +(11-1)xc = a +10c ,
A21 = a +(21-1)xc = a +20c
A1 +A11+A21 = 3a + 30c = 99
a + 10c = 33
A3 + A19 = a + 2c + a + 18c
A3 + A19 = 2a +20c
A3 + A19 = 2(a +10c)
A3 + A19 = 2 x 33
A3 + A19 = 66
User avatar
kelly_jacques
User avatar
Joined: 16 Apr 2023
Last visit: 10 Jul 2023
Posts: 36
Given Kudos: 107
Location: Canada
Posts: 36
Kudos: 0
In the sequence a1, a2, ... , an each term after the first term is 06 Jun 2023, 06:46
Kudos
Add Kudos
Bookmarks
Bookmark this Post
chetan2u Could you please clarify why you assume that c is 1? I tried the same methodology but got stuck because my equation was 3a + 30c = 99 so I had two variables.

My mentality was
a2 = a1 + c
a3 = a1 + c + c (so a1 +2c)
a4 = a1 + c + c + c (so a1 + 3c)
etc
User avatar
MyNameisFritz
User avatar
Joined: 10 May 2024
Last visit: 18 Aug 2025
Posts: 46
Own Kudos:
25
Given Kudos: 169
Location: Latvia
GMAT Focus 1: 555 Q75 V79 DI79
GMAT Focus 1: 555 Q75 V79 DI79
Posts: 46
Kudos: 25
In the sequence a1, a2, ... , an each term after the first term is 27 Jun 2024, 23:30
Kudos
Add Kudos
Bookmarks
Bookmark this Post
a1 = x
a2 = x + c
a3 = x +2c
and so on
so a1 + a11 + a21 = x + x +10c + x + 20c = 99
3x + 30c = 99
x + 10c = 33

a3 + a19 = x + 2c + x +18c = 2x +20c
if x+10c = 33, 2x + 20c will be twice that, so 66

Answer A
Moderators:
Bunuel
Math Expert
109818 posts
Krunaal
Tuck School Moderator
853 posts