How old is he now?

Expert replies

neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 amFollowed by: 52 members; Location: Utrecht, The Netherlands; Thanked: 318 times

by neelgandham » Tue Jan 17, 2012 6:21 am

A Trussian's weight, in keils, can be calculated by taking the square root of his age in years. A Trussianteenager now weighs three keils less than he will seventeen years after he is twice as old as he is now. How old is he now?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18

Source: A local-GMAT-prep-company's material

Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/

Like this post

Source: Beat The GMAT — Problem Solving | Tue Jan 17, 2012 6:21 am

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Tue Jan 17, 2012 6:41 am

Start with answer choices

Choice C:

If his current age = 16, weight = 4

17 + 2(16) = 49, weight = 7

Difference = 7-4 = 3 - Satisfies given condition. C IMO

Like this post

GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Tue Jan 17, 2012 6:48 am

neelgandham wrote:A Trussian's weight, in keils, can be calculated by taking the square root of his age in years. A Trussianteenager now weighs three keils less than he will seventeen years after he is twice as old as he is now. How old is he now?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18

Source: A local-GMAT-prep-company's material

Ages
Let today's age = T
So, 17 years after he is twice as old as he is now = 2T + 17

Weights
Today's weight = root(T)
Future weight = root(2T + 17)

Big step
A Trussianteenager now weighs three keils less than he will seventeen years after he is twice as old as he is now.
This tells us that: root(T) + 3 = root(2T + 17)

Solve for T
Square both sides: T + 6root(T) + 9 = 2T + 17
Simplify: 6root(T) = T + 8

At this point, we can see that T must be a perfect square. So, we'll check the answer choices for perfect squares.

C --> If T = 16, we get 6root(16) = 16 + 8
Simplify to get 24 = 24

Answer = C

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

chieftang: Master | Next Rank: 500 Posts; Posts: 218; Joined: Wed Nov 23, 2011 8:05 pmFollowed by: 4 members; Thanked: 26 times

by chieftang » Tue Jan 17, 2012 9:46 am

Pretty good question.

I ended up with a quadratic eqn T^2 - 20T + 64 = 0, factored to (T-16)(T-4)=0, and threw out the soln 4 without further thought since it wasn't an answer choice. Interestingly, though, that soln is the weight... But that left me with T=16 for the age. Answer C

Chieftang's Combinatorics Notes
Mediant Fractions
Harmonic Mean

Like this post

ronnie1985: Legendary Member; Posts: 626; Joined: Fri Dec 23, 2011 2:50 amFollowed by: 10 members; Location: Ahmedabad; Thanked: 31 times

by ronnie1985 » Wed Jan 18, 2012 12:36 am

If the age of T is x then weight is âˆšx.
The given conditions can be converted into the equation,
âˆš(2x+17) - 3 = âˆšx
Solving we get x = 16 or 4
Since T is teenager, he is 16 years of age.

Follow your passion, Success as perceived by others shall follow you

Like this post

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Wed Jan 18, 2012 11:08 am

neelgandham wrote:A Trussian's weight, in keils, can be calculated by taking the square root of his age in years. A Trussianteenager now weighs three keils less than he will seventeen years after he is twice as old as he is now. How old is he now?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18

Source: A local-GMAT-prep-company's material

ALWAYS LOOK AT THE ANSWER CHOICES.

When a GMAT question involves a real-world situation, the implied values will be realistic.
The number of dogs sold will be an integer; the weight of a person will not be a radical.
How could a scale in the real world register a weight of 10âˆš2 or 8âˆš3?
Thus, since the current weight of the teenager is the square root of the correct answer, the only viable answer choice here is C.

The correct answer is C.

If we wanted to be very, very safe, we could quickly plug in answer choice C:
Current weight = âˆš16 = 4.
17 years after he is twice as old = 17 + 2*16 = 49, implying a weight of 7.
Weight difference = 7-4 = 3.
Success!

Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

Like this post

hazelnut01: Master | Next Rank: 500 Posts; Posts: 157; Joined: Sat Nov 19, 2016 5:34 amFollowed by: 4 members; Thanked: 2 times

by hazelnut01 » Thu Mar 30, 2017 6:17 pm

neelgandham wrote:A Trussian's weight, in keils, can be calculated by taking the square root of his age in years. A Trussian teenager now weighs three keils less than he will seventeen years after he is twice as old as he is now. How old is he now?
(A) 14 (B) 15 (C) 16 (D) 17 (E) 18

Source: Manhattan Challenge Problems (2002, October 7 - Weighty Years)

Let us call the Trussian's current age a. Why my equation incorrect? 17âˆ’3âˆša=2a?

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] » Fri Mar 31, 2017 9:23 am

Hi ziyuenlau,

This question can be solved rather easily by TESTing THE ANSWERS. If you're going to approach it algebraically though, then you have to be careful about whether your variables are referring to age OR weight.

According to the prompt, age is in YEARS and weight is in SQUARE-ROOT of YEARS.

For example:
X = age (in years)
âˆšX = weight (in kiels)

The phrase "A Trussian teenager now WEIGHS three keils less than he will seventeen years after he is twice as old as he is now" focuses on the current WEIGHT relative to a future WEIGHT, so we're going to need a couple of square-root signs. It translates into:

âˆšX = âˆš(2X+17) - 3

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

Contact Rich at [email protected]

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

563 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (563 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