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

 It is currently 20 Aug 2018, 09:42

### 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

# If N is a positive integer, what is the last digit of 1! +

Author Message
Current Student
Joined: 11 May 2008
Posts: 551
If N is a positive integer, what is the last digit of 1! +  [#permalink]

### Show Tags

27 Aug 2008, 20:38
If N is a positive integer, what is the last digit of 1! + 2! + ... + N! ?

1. N is divisible by 4
2. (N^2 + 1)/5 is an odd integer

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Director
Joined: 23 Sep 2007
Posts: 760

### Show Tags

27 Aug 2008, 21:38
arjtryarjtry wrote:
If N is a positive integer, what is the last digit of 1! + 2! + ... + N! ?

1. N is divisible by 4
2. (N^2 + 1)/5 is an odd integer

C

statement 1 is not suff because 4! = 24, and 8! = 40320

statement 2 is not suff because N could be 2 or 8

together, N must be at least 8

5! = 120, so from 5! and up, every number ends with 0

The statement says "If N is a positive integer", I am assuming that N can be 2
SVP
Joined: 07 Nov 2007
Posts: 1728
Location: New York

### Show Tags

27 Aug 2008, 21:51
arjtryarjtry wrote:
If N is a positive integer, what is the last digit of 1! + 2! + ... + N! ?

1. N is divisible by 4
2. (N^2 + 1)/5 is an odd integer

1. N is divisible by 4

--> N>=4
1! + 2! +3!+4!+.
= 1+2+6+24 + 5!+..n!
=33+ (any factorial >=5! ends with zero as last digit)

N=4 last digit 3
N=8 when you add 33 to any number with last digit 0 --> last digit must be '3"

Suffcient

2. (N^2 + 1)/5
N=2,8,32, ....
When n=2 1!+2! = 3 (last digit 3)
n=8 last digit must be 3 as discussed above.
n=32

suffcieint

D

What is OA.
_________________

Smiling wins more friends than frowning

Manager
Joined: 09 Jul 2007
Posts: 233

### Show Tags

27 Aug 2008, 22:24
Good catch suresh ..
Director
Joined: 23 Sep 2007
Posts: 760

### Show Tags

27 Aug 2008, 22:45
good catch suresh, it would be great if people can have you standing behind them during the real test to catch their mistakes before they click NEXT.
SVP
Joined: 07 Nov 2007
Posts: 1728
Location: New York

### Show Tags

27 Aug 2008, 22:50
gmatnub wrote:
good catch suresh, it would be great if people can have you standing behind them during the real test to catch their mistakes before they click NEXT.

I can trade "standing behind anyone for QUANT " for "someone standing behind me for Verbal (especially RC)"

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

_________________

Smiling wins more friends than frowning

Re: factorial &nbs [#permalink] 27 Aug 2008, 22:50
Display posts from previous: Sort by

# If N is a positive integer, what is the last digit of 1! +

Moderator: chetan2u

# Events & Promotions

 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®.