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

 It is currently 21 Jan 2019, 04:42

### 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 January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
• ### GMAT Club Tests are Free & Open for Martin Luther King Jr.'s Birthday!

January 21, 2019

January 21, 2019

10:00 PM PST

11:00 PM PST

Mark your calendars - All GMAT Club Tests are free and open January 21st for celebrate Martin Luther King Jr.'s Birthday.
• ### The winners of the GMAT game show

January 22, 2019

January 22, 2019

10:00 PM PST

11:00 PM PST

In case you didn’t notice, we recently held the 1st ever GMAT game show and it was awesome! See who won a full GMAT course, and register to the next one.

# Given an arithmetic sequence of N terms in which the common difference

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 52342
Given an arithmetic sequence of N terms in which the common difference  [#permalink]

### Show Tags

26 Mar 2018, 22:26
00:00

Difficulty:

25% (medium)

Question Stats:

85% (00:39) correct 15% (00:33) wrong based on 36 sessions

### HideShow timer Statistics

Given an arithmetic sequence of N terms in which the common difference between terms is 2, what is the value of N?

(1) The first term is 18.
(2) The last term is 70.

_________________
Senior PS Moderator
Status: It always seems impossible until it's done.
Joined: 16 Sep 2016
Posts: 670
Re: Given an arithmetic sequence of N terms in which the common difference  [#permalink]

### Show Tags

26 Mar 2018, 23:17
Bunuel wrote:
Given an arithmetic sequence of N terms in which the common difference between terms is 2, what is the value of N?

(1) The first term is 18.
(2) The last term is 70.

Some theory on the AP (arithmetic progressions)

$$x_n = a+d (n-1)$$

Where x_n is the nth term. a is the first term, n is the number of terms & d is the common difference.

So here we are asked to find the no. of terms or n.

(1) The first term is 18. We do not know how long the series is just based on the starting point. Not sufficient
(2) The last term is 70. We do not know how long the series is just based on the ending point. Not sufficient

At this point it can be either (C) both options together work or (E) nothing works.

Let's see,
(1) + (2) -> we know the starting point and the ending point both! Also we are given the difference between any two successive elements. Hence Sufficient.

Option (C) is correct.

Best,
_________________

Regards,

“Do. Or do not. There is no try.” - Yoda (The Empire Strikes Back)

Senior Manager
Joined: 29 Dec 2017
Posts: 386
Location: United States
Concentration: Marketing, Technology
GMAT 1: 630 Q44 V33
GMAT 2: 690 Q47 V37
GMAT 3: 710 Q50 V37
GPA: 3.25
WE: Marketing (Telecommunications)
Given an arithmetic sequence of N terms in which the common difference  [#permalink]

### Show Tags

29 Mar 2018, 13:44
Bunuel wrote:
Given an arithmetic sequence of N terms in which the common difference between terms is 2, what is the value of N?

(1) The first term is 18.
(2) The last term is 70.

For any arithmetic sequence a(n)=a1+(n-1)d, and we are given d=2.
So we have 4 variables and 2 equations, and we need 2 more variables/equations to solve the problem.
--> Highly likely that the answer is C

(1) NS, gives us only 1 variable
(2) NS, gives us only 1 variable

(1)+(2) Sufficient, as we got 2 variable, and this is enough.
Given an arithmetic sequence of N terms in which the common difference &nbs [#permalink] 29 Mar 2018, 13:44
Display posts from previous: Sort by