BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

units digit of (n + 2)^2

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

units digit of (n + 2)^2

by sanju09 » Fri Jan 28, 2011 3:56 am
n is an integer. If the units digit of n^2 is 5, what is the units digit of (n + 2)^2?
(A) 0
(B) 1
(C) 4
(D) 5
(E) 9



for beginners
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
Top
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Fri Jan 28, 2011 4:08 am
sanju09 wrote:n is an integer. If the units digit of n^2 is 5, what is the units digit of (n + 2)^2?
(A) 0
(B) 1
(C) 4
(D) 5
(E) 9
As the unit's digit of n² is 5, unit's digit of n is also 5.
Hence, unit's digit of (n + 2) is 7.

Therefore, unit's digit of (n + 2)² will be unit's digit of 7*7 = 49, i.e. 9.

The correct answer is E.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

by sanju09 » Fri Jan 28, 2011 4:36 am
Anurag@Gurome wrote:
sanju09 wrote:n is an integer. If the units digit of n^2 is 5, what is the units digit of (n + 2)^2?
(A) 0
(B) 1
(C) 4
(D) 5
(E) 9
As the unit's digit of n² is 5, unit's digit of n is also 5.
Hence, unit's digit of (n + 2) is 7.

Therefore, unit's digit of (n + 2)² will be unit's digit of 7*7 = 49, i.e. 9.

The correct answer is E.
right answer by chance...

if units digit of integer n is 5, then n could be either positive or negative, and units digit of integer n + 2 is 7 when n is positive, but it's 3 if n is negative, but in both cases units digit of integer n^2 is always 9.
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
Top
Senior | Next Rank: 100 Posts
Posts: 45
Joined: Sun Oct 16, 2011 2:21 pm
Followed by:1 members

by lenagmat » Tue Oct 25, 2011 11:25 am
Is it ALWAYS:
As the unit's digit of n² is 5, unit's digit of n is also 5.

I mean if the unit's digit of n^2 is 9, unit's digit of n is also 9??

Anurag@Gurome wrote:
sanju09 wrote:
As the unit's digit of n² is 5, unit's digit of n is also 5.
Top
Post new topic Post Reply
• Page 1 of 1