• NEW! FREE Beat The GMAT Quizzes
    NEW! FREE Beat The GMAT Quizzes
    NEW! FREE Beat The GMAT Quizzes
    Hundreds of Questions Highly Detailed Reporting Expert Explanations TAKE A FREE GMAT QUIZ
  • 7 CATs FREE!
    If you earn 100 Forum Points

    Engage in the Beat The GMAT forums to earn
    100 points for $49 worth of Veritas practice GMATs FREE

    Veritas Prep
    VERITAS PRACTICE GMAT EXAMS
    Earn 10 Points Per Post
    Earn 10 Points Per Thanks
    Earn 10 Points Per Upvote
    REDEEM NOW

Arnold and Danny are two twin brothers that are...

This topic has 3 expert replies and 0 member replies

Arnold and Danny are two twin brothers that are...

Post
Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 9 from the product of their ages a year from today. What is their age today?

A. 2
B. 4
C. 5
D. 7
E. 9

The OA is B.

Please, can any expert explain this PS question for me? I tried to solve it but I can't get the correct answer. i can't define the correct equation to solve it. I need your help. Thanks.

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Top Reply
Post
Quote:
Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 9 from the product of their ages a year from today. What is their age today?

A. 2
B. 4
C. 5
D. 7
E. 9

The OA is B.

Please, can any expert explain this PS question for me? I tried to solve it but I can't get the correct answer. i can't define the correct equation to solve it. I need your help. Thanks.
Hi swerve,
Let's take a look at your question.

Let age of twin brothers be x today then after a year their age will be x + 1.
The product of their ages today is smaller by 9 from the product of their ages a year from today. It can be written as:
$$\left(x+1\right)^2-9=x^2$$
$$x^2+2x+1-9=x^2$$
$$2x+1-9=0$$
$$2x-8=0$$
$$2x=8$$
$$x=\frac{8}{2}=4$$

Therefore, Option B is correct.

Hope it helps.
I am available if you'd like any follow up.

_________________
GMAT Prep From The Economist
We offer 70+ point score improvement money back guarantee.
Our average student improves 98 points.

  • +1 Upvote Post
  • Quote
  • Flag
Free 7-Day Test Prep with Economist GMAT Tutor - Receive free access to the top-rated GMAT prep course including a 1-on-1 strategy session, 2 full-length tests, and 5 ask-a-tutor messages. Get started now.

GMAT/MBA Expert

Elite Legendary Member
Joined
23 Jun 2013
Posted:
10197 messages
Followed by:
497 members
Upvotes:
2867
GMAT Score:
800
Post
Hi swerve,

We're told that Arnold and Danny are TWIN brothers who are celebrating their birthdays and the product of their ages TODAY is 9 less than the product of their ages a year from today. We're asked for their ages TODAY. This question can be solved by TESTing the ANSWERS.

Since Arnold and Danny are TWINS, they have the SAME age. Let's start with Answer B...

Answer B: 4 years old
Product of the ages TODAY = (4)(4) = 16
Product of their ages in ONE YEAR = (5)(5) = 25
The difference in products is 25 - 16 = 9
This is an exact match for what we were told, so this MUST be the answer.

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

_________________
Contact Rich at Rich.C@empowergmat.com

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post
swerve wrote:
Arnold and Danny are two twin brothers that are celebrating their birthday. The product of their ages today is smaller by 9 from the product of their ages a year from today. What is their age today?

A. 2
B. 4
C. 5
D. 7
E. 9
If we let Arnold's and Danny’s age today = n, then their ages one year from today will be (n + 1). Thus, we have:

n^2 + 9 = (n + 1)(n + 1)

n^2 + 9 = n^2 + 2n + 1

8 = 2n

4 = n

Answer: B

_________________

Jeffrey Miller
Head of GMAT Instruction
jeff@targettestprep.com



See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

  • +1 Upvote Post
  • Quote
  • Flag
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

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

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

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

    Available with Beat the GMAT members only code

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

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • The Princeton Review
    FREE GMAT Exam
    Know how you'd score today for $0

    Available with Beat the GMAT members only code

    MORE DETAILS
    The Princeton Review

Top First Responders*

1 Ian Stewart 44 first replies
2 Brent@GMATPrepNow 33 first replies
3 Scott@TargetTestPrep 32 first replies
4 Jay@ManhattanReview 24 first replies
5 GMATGuruNY 18 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

Most Active Experts

1 image description Scott@TargetTestPrep

Target Test Prep

149 posts
2 image description Max@Math Revolution

Math Revolution

93 posts
3 image description Ian Stewart

GMATiX Teacher

53 posts
4 image description Brent@GMATPrepNow

GMAT Prep Now Teacher

50 posts
5 image description GMATGuruNY

The Princeton Review Teacher

30 posts
See More Top Beat The GMAT Experts