• Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep

don't understand the explanation in OG to this problem

This topic has 1 expert reply and 2 member replies
isisalaska Community Manager Default Avatar
Joined
10 Dec 2006
Posted:
363 messages
Followed by:
2 members
Upvotes:
7

don't understand the explanation in OG to this problem

Post Sun Jan 07, 2007 10:37 am
Hi, could anyone give me a better explanation to this problem?:
If a is a positive and if the unit digit of a^2 is 9 and (a+1)^2 is 4, what is (a+2)^2

Thanks!

_________________
Isis Alaska

  • +1 Upvote Post
  • Quote
  • Flag
Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!

GMAT/MBA Expert

Stacey Koprince GMAT Instructor
Joined
27 Dec 2006
Posted:
2228 messages
Followed by:
680 members
Upvotes:
639
GMAT Score:
780
Top Reply
Post Fri Jan 26, 2007 11:47 pm
Raj is right. If the units digit of a^2 is 9, only two numbers will square to give a units digit of 9: 3 or 7. See below.

Units digit when squaring:
0^2 = 0
1^2 = 1
2^2 = 4
3^2 = 9
4^2 = 6
5^2 = 5
6^2 = 6
7^2 = 9
8^2 = 4
9^2 = 1

So, a is either 3 or 7. If (a+1)^2 units digit is 4, then a must be 7, because (7+1)^2 = 8^2 = units digit of 4. a can't be 3, b/c (3+1)^2 = 4^2 = units digit of 6.

So if a is 7, then (a+2) = 9. 9^2 = units digit of 1.

_________________
Please note: I do not use the Private Messaging system! I will not see any PMs that you send to me!!

Stacey Koprince
GMAT Instructor
Director of Online Community
Manhattan GMAT

Contributor to Beat The GMAT!

Learn more about me

  • +1 Upvote Post
  • Quote
  • Flag
Free Manhattan Prep online events - The first class of every online Manhattan Prep course is free. Classes start every week.
axefx Newbie | Next Rank: 10 Posts Default Avatar
Joined
01 Dec 2006
Posted:
9 messages
Top Reply
Post Thu Jan 25, 2007 11:57 am
rajs.kumar wrote:
I assume the question asks for the unit digit of (a+2) ^ 2.

if unit digit of a ^ 2 is 9 then unit place a should be 3 or 7

if unit digit of (a+1) ^ 2 is 4 then unit place can only be 8

=> unit digit of (a+2) ^ 2 is 1

Hope this helps.
can you please elaborate... your analysis seems to have a ton of holes... how do the first two statements conclude into the third one!?

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Stacey Koprince GMAT Instructor
Joined
27 Dec 2006
Posted:
2228 messages
Followed by:
680 members
Upvotes:
639
GMAT Score:
780
Post Fri Jan 26, 2007 11:47 pm
Raj is right. If the units digit of a^2 is 9, only two numbers will square to give a units digit of 9: 3 or 7. See below.

Units digit when squaring:
0^2 = 0
1^2 = 1
2^2 = 4
3^2 = 9
4^2 = 6
5^2 = 5
6^2 = 6
7^2 = 9
8^2 = 4
9^2 = 1

So, a is either 3 or 7. If (a+1)^2 units digit is 4, then a must be 7, because (7+1)^2 = 8^2 = units digit of 4. a can't be 3, b/c (3+1)^2 = 4^2 = units digit of 6.

So if a is 7, then (a+2) = 9. 9^2 = units digit of 1.

_________________
Please note: I do not use the Private Messaging system! I will not see any PMs that you send to me!!

Stacey Koprince
GMAT Instructor
Director of Online Community
Manhattan GMAT

Contributor to Beat The GMAT!

Learn more about me

  • +1 Upvote Post
  • Quote
  • Flag
Free Manhattan Prep online events - The first class of every online Manhattan Prep course is free. Classes start every week.

Best Conversation Starters

1 lheiannie07 116 topics
2 LUANDATO 67 topics
3 swerve 66 topics
4 ardz24 61 topics
5 AAPL 59 topics
See More Top Beat The GMAT Members...

Most Active Experts

1 image description Scott@TargetTestPrep

Target Test Prep

213 posts
2 image description Brent@GMATPrepNow

GMAT Prep Now Teacher

177 posts
3 image description Jeff@TargetTestPrep

Target Test Prep

168 posts
4 image description Rich.C@EMPOWERgma...

EMPOWERgmat

133 posts
5 image description GMATGuruNY

The Princeton Review Teacher

126 posts
See More Top Beat The GMAT Experts