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

Expert replies

swerve: Legendary Member; Posts: 2535; Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

by swerve » Sat Jan 20, 2018 7:24 am

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.

Like this post

Source: Beat The GMAT — Problem Solving | Sat Jan 20, 2018 7:24 am

EconomistGMATTutor: GMAT Instructor; Posts: 555; Joined: Wed Oct 04, 2017 4:18 pmFollowed by: 12 members; Thanked: 180 times

by EconomistGMATTutor » Sat Jan 20, 2018 1:07 pm

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.

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Mon Jan 22, 2018 2:35 pm

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 [email protected]

Like this post

Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

by Jeff@TargetTestPrep » Mon Jan 29, 2018 9:51 am

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
[email protected]

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

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review