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

 It is currently 21 Feb 2019, 12:40

### 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

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

## Events & Promotions

###### Events & Promotions in February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
• ### Online GMAT boot camp for FREE

February 21, 2019

February 21, 2019

10:00 PM PST

11:00 PM PST

Kick off your 2019 GMAT prep with a free 7-day boot camp that includes free online lessons, webinars, and a full GMAT course access. Limited for the first 99 registrants! Feb. 21st until the 27th.
• ### Free GMAT RC Webinar

February 23, 2019

February 23, 2019

07:00 AM PST

09:00 AM PST

Learn reading strategies that can help even non-voracious reader to master GMAT RC. Saturday, February 23rd at 7 AM PT

# Series T is a sequence of numbers where each term after the

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

### Hide Tags

Manager
Joined: 27 Oct 2009
Posts: 119
Location: Montreal
Schools: Harvard, Yale, HEC
Series T is a sequence of numbers where each term after the  [#permalink]

### Show Tags

30 Dec 2010, 10:53
2
18
00:00

Difficulty:

25% (medium)

Question Stats:

80% (02:35) correct 20% (02:35) wrong based on 327 sessions

### HideShow timer Statistics

Series T is a sequence of numbers where each term after the first term is x greater than the term that precedes it. If the sum of the first and last terms of series T is 14, then what is the sum of the first three terms of series T and the last three terms of series T?

A. -7
B. 7
C. 14
D. 42
E. 84
Math Expert
Joined: 02 Sep 2009
Posts: 53063
Re: Kaplan Sequence Teaser  [#permalink]

### Show Tags

30 Dec 2010, 11:21
7
7
ezinis wrote:
Series T is a sequence of numbers where each term after the first term is x greater than the term that precedes it. If the sum of the first and last terms of series T is 14, then what is the sum of the first three terms of series T and the last three terms of series T?
A) -7
B) 7
C) 14
D) 42
E) 84

T is an evenly spaced set. For evenly spaced set $$a_1+a_n=a_2+a_{n-1}=a_3+a_{n-2}=...$$, so if given that $$a_1+a_n=14$$ then $$(a_1+a_n)+(a_2+a_{n-1})+(a_3+a_{n-2})=3*14=42$$.

_________________
##### General Discussion
Manager
Joined: 27 Oct 2009
Posts: 119
Location: Montreal
Schools: Harvard, Yale, HEC
Re: Kaplan Sequence Teaser  [#permalink]

### Show Tags

30 Dec 2010, 12:07
Bravo, I found my mistake thanks to you. I was obsessing about "x times greater ...". But I solved it. So lets pretend the stem says ... x times greater ... Can someone give a solution to approach this?
Math Expert
Joined: 02 Sep 2009
Posts: 53063
Re: Kaplan Sequence Teaser  [#permalink]

### Show Tags

30 Dec 2010, 13:33
1
ezinis wrote:
Bravo, I found my mistake thanks to you. I was obsessing about "x times greater ...". But I solved it. So lets pretend the stem says ... x times greater ... Can someone give a solution to approach this?

You won't get the answer in this case, as you can not calculate: $$a+ax+ax^2+ax^{n-3}+ax^{n-2}+ax^{n-1}$$ just knowing that $$a+ax^{n-1}=14$$
_________________
Manager
Status: ==GMAT Ninja==
Joined: 08 Jan 2011
Posts: 194
Schools: ISB, IIMA ,SP Jain , XLRI
WE 1: Aditya Birla Group (sales)
WE 2: Saint Gobain Group (sales)
Re: Kaplan Sequence Teaser  [#permalink]

### Show Tags

08 Jan 2011, 22:20
3
my way of solving
a+l = 14
now the series would be a,a+d,a+2d...........l-2d,l-d,l
now the sum of the first three terms and last three terms would be a+a+d+a+2d+l-2d+l-d+l
which comes out to be 3 (a+l) = 3 (14) = 42
I hope this is the easiest method of solving the question...
_________________

WarLocK
_____________________________________________________________________________
The War is oNNNNNNNNNNNNN for 720+
see my Test exp here http://gmatclub.com/forum/my-test-experience-111610.html
do not hesitate me giving kudos if you like my post.

Current Student
Joined: 03 Sep 2012
Posts: 380
Location: United States
Concentration: Healthcare, Strategy
GMAT 1: 730 Q48 V42
GPA: 3.88
WE: Medicine and Health (Health Care)
Re: Kaplan Sequence Teaser  [#permalink]

### Show Tags

28 Sep 2012, 04:15
2
This is the way i solved it ..

The question gives us a general formula that confirms that we are dealing with an A.P. , therefore we know that the nth term = a (n-1)d .. In this case d = x ...

First term of the AP = A ; Last term = L ..

we know that A + L = 14 ...........[I]

Now we are to find the sum of 6 terms , ie the first three and the last three ... Lets assume that this series has 6 numbers .. therefore Sum of 6 numbers can be written as

S6 = 6/2 [ A + L ]

= 3 x 14 ( From I)

= 42 (D)

As an alternative to this method , we could PLUG IN values for X and solve for the sum of 6 terms of the AP as follows ------------->

Let us assume x =1 , therefore we would need to come up with a sequence whose first and last term adds to 14 , and which as at least 6 terms ...

let us use this sequence ...

3 , 4 , 5, 6, 7, 8, 9, 10, 11

The first and the last terms add to 14 ...

Each term is x greater than the one it succeeds ( in this case i have assumed x to be 01)

The first three and the last three terms are : 3 + 4 + 5 + 9 + 10 + 11 = 42 (D)

To further test the plug in method (not required to confirm the answer but just to test it out) ...

Now let us assume that x = 2

1 3 5 7 9 11 13

First three and last three terms add up to = 42 (D) ....
_________________

"When you want to succeed as bad as you want to breathe, then you’ll be successful.” - Eric Thomas

Intern
Joined: 04 Mar 2011
Posts: 13
Re: Series T is a sequence of numbers where each term after the  [#permalink]

### Show Tags

26 Sep 2014, 07:29
this is the way i solved it though it is long and took me over 5 mins. I guess Bunnel's method is best. Here is mine:

series is k, k+x, k+2x.......k+(n-1)x
sum of first and the last term is therefore k + k+(n-1)x = 14

summing first three members of the set, we have: k + k+x + k+2x = 3(k+x)--------(1)

summing the last 3 members of the set we have: k+(n-1)x + k+(n-2)x + k+(n-3)x = 3k+(3n-6)x ------(2)

(1)+(2) we have : 3[2k+(n-1)x]
the item in [] was given as 14

hence answer is 3*[14] = 42 .....(D)
Current Student
Status: Remember to Always Think Twice
Joined: 04 Nov 2014
Posts: 54
Location: India
GMAT 1: 740 Q49 V40
GPA: 3.51
Re: Series T is a sequence of numbers where each term after the  [#permalink]

### Show Tags

24 Feb 2016, 06:28
Since no information is given about the first term, x, and anything else,
assume first term = 1; hence last term = 13,
so, 1 3 5 7 9 11 13 will suffice the series in which x = 2, from here answer is 42
also, 1 2 3 4 5 6 7 8 9 10 11 12 13 also suffices, where x = 1, from which the answer is again 42
bingo!!
(Saves time)
_________________

breathe in.. and breathe out!

Intern
Joined: 01 Feb 2016
Posts: 9
Location: Viet Nam
GMAT 1: 500 Q49 V15
GMAT 2: 680 Q49 V34
WE: Real Estate (Real Estate)
Re: Series T is a sequence of numbers where each term after the  [#permalink]

### Show Tags

24 Feb 2016, 10:02
a1+a1+x+a1+2x+an+an-x+an-2x=3(a1+an)=3*14=42
VP
Joined: 07 Dec 2014
Posts: 1153
Series T is a sequence of numbers where each term after the  [#permalink]

### Show Tags

02 Aug 2018, 20:28
ezinis wrote:
Series T is a sequence of numbers where each term after the first term is x greater than the term that precedes it. If the sum of the first and last terms of series T is 14, then what is the sum of the first three terms of series T and the last three terms of series T?

A. -7
B. 7
C. 14
D. 42
E. 84

if first three terms and last three terms are to sum differently,
then sequence needs a minimum of four terms
assume four terms: t1, t1+x, t1+2x, t1+3x
t1+(t1+3x)=14→
2*t1+3x=14
assuming t1 and x are positive integers,
then t1=4 and x=2
sequence=4, 6, 8, 10
sum of first 3 terms=18
sum of last 3 terms=24
combined sum=42
D
Manager
Joined: 12 Sep 2017
Posts: 139
Re: Series T is a sequence of numbers where each term after the  [#permalink]

### Show Tags

27 Jan 2019, 14:29
Hello Bunuel

Could you please tell me if my reasoning is good here?

Avg = 7

7 x 6 terms = 42

Because I am seeing that everybody is just multiplying 14 x 3 so I think I am doing something wrong.

Kind regards!
Re: Series T is a sequence of numbers where each term after the   [#permalink] 27 Jan 2019, 14:29
Display posts from previous: Sort by

# Series T is a sequence of numbers where each term after the

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

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.