What is the last digit of : DS Archive
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 18 Jan 2017, 18:21

### 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 June
Open Detailed Calendar

# What is the last digit of

Author Message
Intern
Joined: 25 Oct 2009
Posts: 24
Schools: Wharton, HBS, Stanford
Followers: 0

Kudos [?]: 38 [0], given: 12

What is the last digit of [#permalink]

### Show Tags

11 Jan 2010, 13:50
00:00

Difficulty:

(N/A)

Question Stats:

50% (00:00) correct 50% (00:33) wrong based on 6 sessions

### HideShow timer Statistics

What is the last digit of $$9^1+99^2+999^3+...+(10^n-1)^n$$?

(1) n is even
(2) n is prime

OA is
[Reveal] Spoiler:
A

OE:
[Reveal] Spoiler:
We have the sum of integers:

$$(..9) + (..1) + (..9) + (..1) + ...$$

Statement (1) by itself is sufficient. If n is even then this sum ends with 0. If it's odd, then this sum ends with 9.

Statement (2) by itself is insufficient. (2 is prime and even, 3 is prime and odd)

Question:
[Reveal] Spoiler:
it seems from question's stem that n>3, which combined with Statement (2) means that n is odd. As a result, the sum always ends with 9. If this correct, the answer should be D.

_________________

KUDOS if you find it helpful

Current Student
Joined: 05 Aug 2008
Posts: 1262
Schools: Ross 2012
WE 1: 5 Years at Fortune 50 Company in Manufacturing
Followers: 20

Kudos [?]: 169 [1] , given: 20

Re: What is the last digit of ...? (GMATClub test m10, q36) [#permalink]

### Show Tags

11 Jan 2010, 16:18
1
KUDOS
You make an interesting point. I think the idea is that N doesn't have to be greater than 3. Although the question has n being at least 3. I think in it's written form, with the ..., N can be one, two, or three. Which is why it is not sufficient.

Also for Data Sufficiency. The two statements cannont be contridictory. So if you were to use like a) and line b) both statements would be contridictory with since the number cannot be prime and even and greater than 3. so your assumption of n>3 is wrong.
_________________
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13441
Followers: 575

Kudos [?]: 163 [0], given: 0

Re: What is the last digit of [#permalink]

### Show Tags

11 Mar 2016, 20:54
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: What is the last digit of   [#permalink] 11 Mar 2016, 20:54
Display posts from previous: Sort by