Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 11 Feb 2016, 05:57

### 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

# If N is an integer, what is the units digit of (N-1)! + N! +

Author Message
Intern
Joined: 03 Aug 2009
Posts: 6
Followers: 0

Kudos [?]: 2 [0], given: 1

If N is an integer, what is the units digit of (N-1)! + N! + [#permalink]  23 Aug 2009, 15:04
00:00

Difficulty:

(N/A)

Question Stats:

100% (06:14) correct 0% (00:00) wrong based on 0 sessions
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If N is an integer, what is the units’
digit of (N-1)! + N! + (N + 1)! + 2^N(3^N+1)?

(1) N > 2
(2) N = 3K + 1, where K is an integer
greater than 1.
Senior Manager
Joined: 23 Jun 2009
Posts: 353
Location: Turkey
Schools: UPenn, UMich, HKS, UCB, Chicago
Followers: 5

Kudos [?]: 110 [1] , given: 63

Re: (N-1)! + N! + (N + 1)! + 2^N(3^N+1) [#permalink]  24 Aug 2009, 05:48
1
KUDOS
Say that as f(n) = $$(N-1)! + N! + (N + 1)!$$ + $$2^N$$.$$(3^N+1)$$
f(1)=0
f(2)=9
f(3)=6
f(4)=2
f(5)=2
for every n>5; f(n)=
if n mod 4 = 0 than 2
if n mod 4 = 1 than 8
if n mod 4 = 2 than 0
if n mod 4 = 3 than 4

A insuff, N>2 does not mean anything
B insuff N=3K+1 does not mean anything (K = 0, N=1, f(n)=0, K=1, N=4, f(n)=2, K=2, N=7, f(n)=4 etc.)
together insuff
we do not know what K is, so f(n) can be any of the results written above.
Re: (N-1)! + N! + (N + 1)! + 2^N(3^N+1)   [#permalink] 24 Aug 2009, 05:48
Display posts from previous: Sort by