GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 16 Jun 2019, 23:59

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.

Close

Request Expert Reply

Confirm Cancel

If the terms of a certain sequence are defined by the equation An

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

 
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 55623
If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 16 Aug 2018, 08:44
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

57% (01:30) correct 43% (01:31) wrong based on 84 sessions

HideShow timer Statistics

Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 7743
If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 16 Aug 2018, 08:51
Bunuel wrote:
If the terms of a certain sequence are defined by the equation \(A_n = A_{n-1} + n\) for all n, what is the value of An in terms of \(A_{n+1}\)?


A. \(A_{n+1} − 1\)

B. \(A_{n+1} + n + 1\)

C. \(A_{n+1} − n\)

D. \(A_{n+1} − n − 1\)

E. \(A_{n+1} − n + 1\)


\(A_n = A_{n-1} + n\)
replace all n by n+1. Don't leave the addition of n
\(A_{n+1} = A_n + n+1\)...
So \(A_n = A_{n+1} - n -1\)

D
_________________
Ask GMAT Experts Forum Moderator
User avatar
V
Status: Preparing for GMAT
Joined: 25 Nov 2015
Posts: 1025
Location: India
GPA: 3.64
GMAT ToolKit User Reviews Badge CAT Tests
Re: If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 16 Aug 2018, 08:54
Bunuel wrote:
If the terms of a certain sequence are defined by the equation \(A_n = A_{n-1} + n\) for all n, what is the value of An in terms of \(A_{n+1}\)?


A. \(A_{n+1} − 1\)

B. \(A_{n+1} + n + 1\)

C. \(A_{n+1} − n\)

D. \(A_{n+1} − n − 1\)

E. \(A_{n+1} − n + 1\)


\(A_{n+1}=A_{n}+n+1\)
\(A_{n}=A_{n+1}-n-1\)
Answer D.
_________________
Please give kudos, if you like my post

When the going gets tough, the tough gets going...
Senior Manager
Senior Manager
User avatar
S
Joined: 12 Sep 2017
Posts: 263
Re: If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 27 Jan 2019, 14:06
chetan2u wrote:
Bunuel wrote:
If the terms of a certain sequence are defined by the equation \(A_n = A_{n-1} + n\) for all n, what is the value of An in terms of \(A_{n+1}\)?


A. \(A_{n+1} − 1\)

B. \(A_{n+1} + n + 1\)

C. \(A_{n+1} − n\)

D. \(A_{n+1} − n − 1\)

E. \(A_{n+1} − n + 1\)


\(A_n = A_{n-1} + n\)
replace all n by n+1. Don't leave the addition of n
\(A_{n+1} = A_n + n+1\)...
So \(A_n = A_{n+1} - n -1\)

D


Hello chetan2u

Why are you replacing all the n's for n + 1?

Kind regards!
Senior Manager
Senior Manager
User avatar
S
Joined: 12 Sep 2017
Posts: 263
Re: If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 27 Jan 2019, 14:25
Bunuel wrote:
If the terms of a certain sequence are defined by the equation \(A_n = A_{n-1} + n\) for all n, what is the value of An in terms of \(A_{n+1}\)?


A. \(A_{n+1} − 1\)

B. \(A_{n+1} + n + 1\)

C. \(A_{n+1} − n\)

D. \(A_{n+1} − n − 1\)

E. \(A_{n+1} − n + 1\)



Hello Bunuel !

Could you please give an explanation regarding this question?

I don't understand how to disappear the An-1.

Kind regards!
Manager
Manager
avatar
B
Joined: 15 Nov 2017
Posts: 54
Re: If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 30 Jan 2019, 01:39
Hi Bunuel,

Could you please explain in more detail how to solve this problem step-by-step?

Thank you so much!

Bunuel wrote:
If the terms of a certain sequence are defined by the equation \(A_n = A_{n-1} + n\) for all n, what is the value of An in terms of \(A_{n+1}\)?


A. \(A_{n+1} − 1\)

B. \(A_{n+1} + n + 1\)

C. \(A_{n+1} − n\)

D. \(A_{n+1} − n − 1\)

E. \(A_{n+1} − n + 1\)
Senior Manager
Senior Manager
User avatar
S
Joined: 12 Sep 2017
Posts: 263
If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 02 Feb 2019, 12:58
1
Hi KHow !

After some time I underdstood it very well by the following:

An = An-1 + n

Let A1 = 1

So given the formula lets calculate the first values:

A1 = 1
A2 = 1+ 2 = 3
A3 = 3 + 3 = 6
A4 = 6 + 4 = 10

So this means that if we want to calculate An+1 it must be An = An+1 - (n+1) = An = An+1 - n - 1.

Ex.

A3 = An+1 - n - 1

A3 = (An+1 = 10) - ((n-1)) = A4 - 1) = (10 - (4+1)) = 6.
Intern
Intern
avatar
B
Joined: 12 Feb 2019
Posts: 2
Re: If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 14 Mar 2019, 15:51
Hey, not sure why it can't be solved this way:

A(n)=A(n-1) + n
A(n-1)= A(n) - n

A(n+1) + A(n-1) = 2A(n)
A(n+1) + A(n) - n = 2A(n)
A(n+1) - n = A(n)

I will be grateful for explanation what I am calculating wrong :)
Manager
Manager
User avatar
Joined: 20 Dec 2013
Posts: 119
Re: If the terms of a certain sequence are defined by the equation An  [#permalink]

Show Tags

New post 14 Mar 2019, 16:16
Bunuel wrote:
If the terms of a certain sequence are defined by the equation \(A_n = A_{n-1} + n\) for all n, what is the value of An in terms of \(A_{n+1}\)?


A. \(A_{n+1} − 1\)

B. \(A_{n+1} + n + 1\)

C. \(A_{n+1} − n\)

D. \(A_{n+1} − n − 1\)

E. \(A_{n+1} − n + 1\)


We can plug in here.

Let n = 3 and A0 = 4

A0 = 4, A1 = 7 A2 = 10 A3 = 13 A4 = 17
So you are looking for A3 = 13 which is 17 - 3 - 1
Hence D
_________________
76000 Subscribers, 7 million minutes of learning delivered and 5.6 million video views

Perfect Scores
http://perfectscores.org
http://www.youtube.com/perfectscores
GMAT Club Bot
Re: If the terms of a certain sequence are defined by the equation An   [#permalink] 14 Mar 2019, 16:16
Display posts from previous: Sort by

If the terms of a certain sequence are defined by the equation An

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne